Category Archives: Bubbles and AntiBubbles

Meltdown: Why our systems fail and What we can do about it

Meltdown: Why our systems fail and What we can do about it

Authors and related work

  • Chris Clearfield 
    • Chris is the founder of System Logic, an independent research and consulting firm focusing on the challenges posed by risk and complexity. He previously worked as a derivatives trader at Jane Street, a quantitative trading firm, in New York, Tokyo, and Hong Kong, where he analyzed and devised mitigations for the financial and regulatory risks inherent in the business of technologically complex high-speed trading. He has written about catastrophic failure, technology, and finance for The Guardian, Forbes, the Harvard Kennedy School Review, the popular science magazine Nautilus, and the Harvard Business Review blog.
  • András Tilcsik
    • András holds the Canada Research Chair in Strategy, Organizations, and Society at the University of Toronto’s Rotman School of Management. He has been recognized as one of the world’s top forty business professors under forty and as one of thirty management thinkers most likely to shape the future of organizations. The United Nations named his course on organizational failure as the best course on disaster risk management in a business school. 
  • How to Prepare for a Crisis You Couldn’t Possibly Predict
    • Over the past five years, we have studied dozens of unexpected crises in all sorts of organizations and interviewed a broad swath of people — executives, pilots, NASA engineers, Wall Street traders, accident investigators, doctors, and social scientists — who have discovered valuable lessons about how to prepare for the unexpected. Here are three of those lessons.

Overview

This book looks at the underlying reasons for accidents that emerge from complexity and how diversity is a fix. It’s based on Charles Perrow’s concept of Normal Accidents being a property of high-risk systems.

Normal Accidents are unpredictable, yet inevitable combinations of small failures that build upon each other within an unforgiving environment. Normal accidents include catastrophic failures such as reactor meltdowns, airplane crashes, and stock market collapses. Though each failure is unique, all these failures have common properties:

    • The system’s components are tightly coupled. A change in one place has rapid consequences elsewhere
    • The system is densely connected, so that the actions of one part affects many others
    • The system’s internals are difficult to observe, so that failure can appear without warning

What happens in all these accidents is that there is misdirected progress in a direction that makes the problem worse. Often, this is because the humans in the system are too homogeneous. They all see the problem from the same perspective, and they all implicitly trust each other (Tight coupling and densely connected).

The addition of diversity is a way to solve this problem. Diversity does three things:

    • It provides additional perspectives into the problem. This only works if there is large enough representation of diverse groups so that they do not succumb to social pressure.
    • It lowers the amount of trust within the group, so that proposed solutions are exposed to a higher level of skepticism.
    • It slows the process down, making the solution less reflexive and more thoughtful.

By designing systems to be transparent, loosely coupled and sparsely connected, the risk of catastrophe is reduced. If that’s not possible, ensure that the people involved in the system are diverse.

My more theoretical thoughts:

There are two factors that affect the response of the network: The level of connectivity and the stiffness of the links. When the nodes have a velocity component, then a sufficiently stiff network (either many somewhat stiff or a few very stiff links) has to move as a single entity. Nodes with sparse and slack connections are safe systems, but not responsive. Stiff, homogeneous (similarity is implicit stiff coupling)  networks are prone to stampede. Think of a ball rolling down a hill as opposed to a lump of jello.

When all the nodes are pushing in the same direction, then the network as a whole will move into more dangerous belief spaces. That’s a stampede. When some percentage of these connections are slack connections to diverse nodes (e.g. moving in other directions), the structure as a whole is more resistant to stampede.

I think that dimension reduction is inevitable in a stiffening network. In physical systems, where the nodes have mass, a stiff structure really only has two degrees of freedom, its direction of travel and its axis of rotation. Which means that regardless of the number of initial dimensions, a stiff body’s motion reduces to two components. Looking at stampedes and panics, I’d say that this is true for behaviors as well, though causality could run in either direction. This is another reason that diversity helps keep away from dangerous conditions, but at the expense of efficiency.

Notes

  • Such a collision should have been impossible. The entire Washington Metro system, made up of over one hundred miles of track, was wired to detect and control trains. When trains got too close to each other, they would automatically slow down. But that day, as Train 112 rounded a curve, another train sat stopped on the tracks ahead—present in the real world, but somehow invisible to the track sensors. Train 112 automatically accelerated; after all, the sensors showed that the track was clear. By the time the driver saw the stopped train and hit the emergency brake, the collision was inevitable. (Page 2)
  • The second element of Perrow’s theory (of normal accidents) has to do with how much slack there is in a system. He borrowed a term from engineering: tight coupling. When a system is tightly coupled, there is little slack or buffer among its parts. The failure of one part can easily affect the others. Loose coupling means the opposite: there is a lot of slack among parts, so when one fails, the rest of the system can usually survive. (Page 25)
  • Perrow called these meltdowns normal accidents. “A normal accident,” he wrote, “is where everyone tries very hard to play safe, but unexpected interaction of two or more failures (because of interactive complexity) causes a cascade of failures (because of tight coupling).” Such accidents are normal not in the sense of being frequent but in the sense of being natural and inevitable. “It is normal for us to die, but we only do it once,” he quipped. (Page 27)
    • This is exactly what I see in my simulations and in modelling with graph Laplacians. There are two factors that affect the response of the network: The level of connectivity and the stiffness of the links. When the nodes have a velocity component, then a sufficiently stiff network (either many somewhat stiff or a few very stiff links) has to behave as a single entity.
  • These were unintended interactions between the glitch in the content filter, Talbot’s photo, other Twitter users’ reactions, and the resulting media coverage. When the content filter broke, it increased tight coupling because the screen now pulled in any tweet automatically. And the news that Starbucks had a PR disaster in the making spread rapidly on Twitter—a tightly coupled system by design. (Page 30)
  • This approach—reducing complexity and adding slack—helps us escape from the danger zone. It can be an effective solution, one we’ll explore later in this book. But in recent decades, the world has actually been moving in the opposite direction: many systems that were once far from the danger zone are now in the middle of it. (Page 33)
  • Today, smartphone videos create complexity because they link things that weren’t always connected (Page 37)
  • For nearly thirty minutes, Knight’s trading system had gone haywire and sent out hundreds of unintended orders per second in 140 stocks. Those very orders had caused the anomalies that John Mueller and traders across Wall Street saw on their screens. And because Knight’s mistake roiled the markets in such a visible way, traders could reverse engineer its positions. Knight was a poker player whose opponents knew exactly what cards it held, and it was already all in. For thirty minutes, the company had lost more than $15 million per minute. (Page 41)
  • Though a small software glitch caused Knight’s failure, its roots lay much deeper. The previous decade of technological innovation on Wall Street created the perfect conditions for the meltdown. Regulation and technology transformed stock trading from a fragmented, inefficient, relationship-based activity to a tightly connected endeavor dominated by computers and algorithms. Firms like Knight, which once used floor traders and phones to execute trades, had to adapt to a new world. (Page 42)
    • This is an important point. There is short-term survival value in becoming homogeneous and tightly connected. Diversity only helps in the long run.
  • As the crew battled the blowout, complexity struck again. The rig’s elaborate emergency systems were just too overwhelming. There were as many as thirty buttons to control a single safety system, and a detailed emergency handbook described so many contingencies that it was hard to know which protocol to follow. When the accident began, the crew was frozen. The Horizon’s safety systems paralyzed them. (Page 49)
    • I think that this may argue opposite to the authors’ point. The complexity here is a form of diversity. The safety system was a high-dimensional system that required an effective user to be aligned with it, like a free climber on a cliff face. A user highly educated in the system could probably have made it work, even better than a big STOP button. But expecting that user is a mistake. The authors actually discuss this later when they describe how safety training was reduced to simple practices that ignored perceived unlikely catastrophic events.
  • “The real threat,” Greenberg explained, “comes from malicious actors that connect things together. They use a chain of bugs to jump from one system to the next until they achieve full code execution.” In other words, they exploit complexity: they use the connections in the system to move from the software that controls the radio and GPS to the computers that run the car itself. “As cars add more features,” Greenberg told us, “there are more opportunities for abuse.” And there will be more features: in driverless cars, computers will control everything, and some models might not even have a steering wheel or brake pedal. (Page 60)
    • In this case it’s not the stiffness of the connections, its the density of connections
  • Attacks on cars, ATMs, and cash registers aren’t accidents. But they, too, originate from the danger zone. Complex computer programs are more likely to have security flaws. Modern networks are rife with interconnections and unexpected interactions that attackers can exploit. And tight coupling means that once a hacker has a foothold, things progress swiftly and can’t easily be undone. In fact, in all sorts of areas, complexity creates opportunities for wrongdoing, and tight coupling amplifies the consequences. It’s not just hackers who exploit the danger zone to do wrong; it’s also executives at some of the world’s biggest companies. (Page 62)
  • By the year 2000, Fastow and his predecessors had created over thirteen hundred specialized companies to use in these complicated deals. “Accounting rules and regulations and securities laws and regulation are vague,” Fastow later explained. “They’re complex. . . . What I did at Enron and what we tended to do as a company [was] to view that complexity, that vagueness . . . not as a problem, but as an opportunity.” Complexity was an opportunity. (Page 69)
    • I’m not sure how to fit this in, but I think there is something here about high-dimensional spaces being essentially invisible. This is the same thing as the safety system on the Deepwater Horizon.
  • But like the core of a nuclear power plant, the truth behind such writing is difficult to observe. And research shows that unobservability is a key ingredient to news fabrications. Compared to genuine articles, falsified stories are more likely to be filed from distant locations and to focus on topics that lend themselves to the use of secret sources, such as war and terrorism; they are rarely about big public events like baseball games. (Page 77)
    •  More heuristics for map building
  • Charles Perrow once wrote that “safety systems are the biggest single source of catastrophic failure in complex, tightly coupled systems.” (Page 85)
    • Dimensions reduce through use, which is a kind of conversation between the users and the designers. Safety systems are rarely used, so this conversation doesn’t happen.
  • Perrow’s matrix is helpful even though it doesn’t tell us what exactly that “crazy failure” will look like. Simply knowing that a part of our system—or organization or project—is vulnerable helps us figure out if we need to reduce complexity and tight coupling and where we should concentrate our efforts. It’s a bit like wearing a seatbelt. The reason we buckle up isn’t that we have predicted the exact details of an impending accident and the injuries we’ll suffer. We wear seatbelts because we know that something unforeseeable might happen. We give ourselves a cushion of time when cooking an elaborate holiday dinner not because we know what will go wrong but because we know that something will. “You don’t need to predict it to prevent it,” Miller told us. “But you do need to treat complexity and coupling as key variables whenever you plan something or build something.” (Page 88)
  • A fundamental feature of complex systems is that we can’t find all the problems by simply thinking about them. Complexity can cause such strange and rare interactions that it’s impossible to predict most of the error chains that will emerge. But before they fall apart, complex systems give off warning signs that reveal these interactions. The systems themselves give us clues as to how they might unravel. (Page 141)
  • Over the course of several years, Rerup conducted an in-depth study of global pharmaceutical powerhouse Novo Nordisk, one of the world’s biggest insulin producers. In the early 1990s, Rerup found, it was difficult for anyone at Novo Nordisk to draw attention to even serious threats. “You had to convince your own boss, his boss, and his boss that this was an issue,” one senior vice president explained. “Then he had to convince his boss that it was a good idea to do things in a different way.” But, as in the childhood game of telephone—where a message gets more and more garbled as it passes between people—the issues became oversimplified as they worked their way up the chain of command. “What was written in the original version of the report . . . and which was an alarm bell for the specialist,” the CEO told Rerup, “was likely to be deleted in the version that senior management read.” (Page 146)
    • Dimension reduction, leading to stampede
  • Once an issue has been identified, the group brings together ad hoc teams from different departments and levels of seniority to dig into how it might affect their business and to figure out what they can do to prevent problems. The goal is to make sure that the company doesn’t ignore weak signs of brewing trouble.  (Page 147)
    • Environmental awareness as a deliberate counter to dimension reduction
  • We show that a deviation from the group opinion is regarded by the brain as a punishment,” said the study’s lead author, Vasily Klucharev. And the error message combined with a dampened reward signal produces a brain impulse indicating that we should adjust our opinion to match the consensus. Interestingly, this process occurs even if there is no reason for us to expect any punishment from the group. As Klucharev put it, “This is likely an automatic process in which people form their own opinion, hear the group view, and then quickly shift their opinion to make it more compliant with the group view.” (Page 154)
    • Reinforcement Learning Signal Predicts Social Conformity
      • Vasily Klucharev
      • We often change our decisions and judgments to conform with normative group behavior. However, the neural mechanisms of social conformity remain unclear. Here we show, using functional magnetic resonance imaging, that conformity is based on mechanisms that comply with principles of reinforcement learning. We found that individual judgments of facial attractiveness are adjusted in line with group opinion. Conflict with group opinion triggered a neuronal response in the rostral cingulate zone and the ventral striatum similar to the “prediction error” signal suggested by neuroscientific models of reinforcement learning. The amplitude of the conflict-related signal predicted subsequent conforming behavioral adjustments. Furthermore, the individual amplitude of the conflict-related signal in the ventral striatum correlated with differences in conforming behavior across subjects. These findings provide evidence that social group norms evoke conformity via learning mechanisms reflected in the activity of the rostral cingulate zone and ventral striatum.
  • When people agreed with their peers’ incorrect answers, there was little change in activity in the areas associated with conscious decision-making. Instead, the regions devoted to vision and spatial perception lit up. It’s not that people were consciously lying to fit in. It seems that the prevailing opinion actually changed their perceptions. If everyone else said the two objects were different, a participant might have started to notice differences even if the objects were identical. Our tendency for conformity can literally change what we see. (Page 155)
    • Gregory Berns
      • Dr. Berns specializes in the use of brain imaging technologies to understand human – and now, canine – motivation and decision-making.  He has received numerous grants from the National Institutes of Health, National Science Foundation, and the Department of Defense and has published over 70 peer-reviewed original research articles.
    • Neurobiological Correlates of Social Conformity and Independence During Mental Rotation
      • Background: When individual judgment conflicts with a group, the individual will often conform his judgment to that of the group. Conformity might arise at an executive level of decision making, or it might arise because the social setting alters the individual’s perception of the world.
      • Methods: We used functional magnetic resonance imaging and a task of mental rotation in the context of peer pressure to investigate the neural basis of individualistic and conforming behavior in the face of wrong information.
      • Results: Conformity was associated with functional changes in an occipital-parietal network, especially when the wrong information originated from other people. Independence was associated with increased amygdala and caudate activity, findings consistent with the assumptions of social norm theory about the behavioral saliency of standing alone.
      • Conclusions: These findings provide the first biological evidence for the involvement of perceptual and emotional processes during social conformity.
      • The Pain of Independence: Compared to behavioral research of conformity, comparatively little is known about the mechanisms of non-conformity, or independence. In one psychological framework, the group provides a normative influence on the individual. Depending on the particular situation, the group’s influence may be purely informational – providing information to an individual who is unsure of what to do. More interesting is the case in which the individual has definite opinions of what to do but conforms due to a normative influence of the group due to social reasons. In this model, normative influences are presumed to act through the aversiveness of being in a minority position
    • A Neural Basis for Social Cooperation
      • Cooperation based on reciprocal altruism has evolved in only a small number of species, yet it constitutes the core behavioral principle of human social life. The iterated Prisoner’s Dilemma Game has been used to model this form of cooperation. We used fMRI to scan 36 women as they played an iterated Prisoner’s Dilemma Game with another woman to investigate the neurobiological basis of cooperative social behavior. Mutual cooperation was associated with consistent activation in brain areas that have been linked with reward processing: nucleus accumbens, the caudate nucleus, ventromedial frontal/orbitofrontal cortex, and rostral anterior cingulate cortex. We propose that activation of this neural network positively reinforces reciprocal altruism, thereby motivating subjects to resist the temptation to selfishly accept but not reciprocate favors.
  • These results are alarming because dissent is a precious commodity in modern organizations. In a complex, tightly coupled system, it’s easy for people to miss important threats, and even seemingly small mistakes can have huge consequences. So speaking up when we notice a problem can make a big difference. (Page 155)
  • KRAWCHECK: I think when you get diverse groups together who’ve got these different backgrounds, there’s more permission in the room—as opposed to, “I can’t believe I don’t understand this and I’d better not ask because I might lose my job.” There’s permission to say, “I come from someplace else, can you run that by me one more time?” And I definitely saw that happen. But as time went on, the management teams became less diverse. And in fact, the financial services industry went into the downturn white, male and middle aged. And it came out whiter, maler and middle-aged-er. (Page 176)
  • “The diverse markets were much more accurate than the homogeneous markets,” said Evan Apfelbaum, an MIT professor and one of the study’s authors. “In homogeneous markets, if someone made a mistake, then others were more likely to copy it,” Apfelbaum told us. “In diverse groups, mistakes were much less likely to spread.” (Page 177)
  • Having minority traders wasn’t valuable because they contributed unique perspectives. Minority traders helped markets because, as the researchers put it, “their mere presence changed the tenor of decision making among all traders.” In diverse markets, everyone was more skeptical. (Page 178)
  • In diverse groups, we don’t trust each other’s judgment quite as much, and we call out the naked emperor. And that’s very valuable when dealing with a complex system. If small errors can be fatal, then giving others the benefit of the doubt when we think they are wrong is a recipe for disaster. Instead, we need to dig deeper and stay critical. Diversity helps us do that. (Page 180)
  • Ironically, lab experiments show that while homogeneous groups do less well on complex tasks, they report feeling more confident about their decisions. They enjoy the tasks they do as a group and think they are doing well. (Page 182)
    • Another stampede contribution
  • The third issue was the lack of productive conflict. When amateur directors were just a small minority on a board, it was hard for them to challenge the experts. On a board with many bankers, one CEO told the researchers, “Everybody respects each other’s ego at that table, and at the end of the day, they won’t really call each other out.” (Page 193)
    • Need to figure out what productive conflict is and how to measure it
  • Diversity is like a speed bump. It’s a nuisance, but it snaps us out of our comfort zone and makes it hard to barrel ahead without thinking. It saves us from ourselves. (Page 197)
  • A stranger is someone who is in a group but not of the group. Simmel’s archetypal stranger was the Jewish merchant in a medieval European town—someone who lived in the community but was different from the insiders. Someone close enough to understand the group, but at the same time, detached enough to have an outsider’s perspective. (Page 199)
    • Can AI be trained to be a stranger?
  • But Volkswagen didn’t just suffer from an authoritarian culture. As a corporate governance expert noted, “Volkswagen is well known for having a particularly poorly run and structured board: insular, inward-looking, and plagued with infighting.” On the firm’s twenty-member supervisory board, ten seats were reserved for Volkswagen workers, and the rest were split between senior managers and the company’s largest shareholders. Both Piëch and his wife, a former kindergarten teacher, sat on the board. There were no outsiders. This kind of insularity went well beyond the boardroom. As Milne put it, “Volkswagen is notoriously anti-outsider in terms of culture. Its leadership is very much homegrown.” And that leadership is grown in a strange place. Wolfsburg, where Volkswagen has its headquarters, is the ultimate company town. “It’s this incredibly peculiar place,” according to Milne. “It didn’t exist eighty years ago. It’s on a wind-swept plain between Hanover and Berlin. But it’s the richest town in Germany—thanks to Volkswagen. VW permeates everything. They’ve got their own butchers, they’ve got their own theme park; you don’t escape VW there. And everybody comes through this system.” (Page 209)
  • Most companies have lots of people with different skills. The problem is, when you bring people together to work on the same problem, if all they have are those individual skills . . . it’s very hard for them to collaborate. What tends to happen is that each individual discipline represents its own point of view. It basically becomes a negotiation at the table as to whose point of view wins, and that’s when you get gray compromises where the best you can achieve is the lowest common denominator between all points of view. The results are never spectacular but, at best, average. (Page 236)
    • The idea here is that there is either total consensus and groupthink, or grinding compromise. The authors are focussing too much on the ends of the spectrum. The environmentally aware, social middle is the sweet spot where flocking occurs.
  • Or think about driverless cars. They will almost certainly be safer than human drivers. They’ll eliminate accidents due to fatigued, distracted, and drunk driving. And if they’re well engineered, they won’t make the silly mistakes that we make, like changing lanes while another car is in our blind spot. At the same time, they’ll be susceptible to meltdowns—brought on by hackers or by interactions in the system that engineers didn’t anticipate. (Page 242)
  • We can design safer systems, make better decisions, notice warning signs, and learn from diverse, dissenting voices. Some of these solutions might seem obvious: Use structured tools when you face a tough decision. Learn from small failures to avoid big ones. Build diverse teams and listen to skeptics. And create systems with transparency and plenty of slack. (Page 242)

When Worlds Collide

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Charlottesville demonstrations, summer 2017 (link)

I’ve been thinking about this picture a lot recently. My research explores how extremist groups can develop using modern computer-mediated communication, particularly recommender systems. This picture lays the main parts like a set of nested puzzle pieces.

This is a picture of a physical event. In August 2017, various “Alt-Right” online communities came to Charlottesville Virginia to ostensibly protest the removal of confederate statues, which in turn was a response to the Charleston South Carolina church shooting of 2015. From August 11th through 12th, sanctioned and unsanctioned protests and counter protests happened in and around Emancipation Park.

Although this is not a runway in Paris, London or New York, this photo contains what I can best call “fashion statements”, in the most serious use of the term. They are mechanisms for signifying and conveying identity,  immediately visible. What are they trying to say to each other and to us, the public behind the camera?

Standing on the right hand of the image is a middle-aged white man, wearing a type of uniform: On his cap and shirt are images of the confederate “battle flag”. He is wearing a military-style camouflage vest and is carrying an AR-15 rifle and a 9mm handgun. These are archetypal components of the Alt-right identity.

He is yelling at a young black man moving in from the left side of the photo, who is also wearing a uniform of a sort. In addition to the black t-shirt and the dreadlocks, he is carrying multiple cameras – the sine qua non of credibility for young black men in modern America. Lastly, he is wearing literal chains and shackles, ensuring that no one will forget the slave heritage behind these protests.

Let’s consider these carried items, the cameras and the guns. The fashion accessories, if you will.

Cameras exist to record a selected instant of reality. It may be framed, with parts left out and others enhanced, but photographs and videos are a compelling document that something in the world happened. Further, these are internet-connected cameras, capable of sharing their content widely and quickly. These two elements, photographic evidence and distribution are a foundation of the #blacklivesmatter movement, which is a response to the wide distribution of videos where American police killed unarmed black men. These videos changed the greater social understanding of a reality encountered by a minority that was incomprehensible by the majority before these videos emerged.

Now to the other accessory, the guns. They are mechanisms “of violence to compel our opponent to fulfil our will”. Unlike cameras, which are used to provide a perspective of reality , these weapons are used to create a reality through their display and their threatened use. They also reflect a perception  of those that wield them that the world has become so threatening that battlefield weapons make sense at a public event.

Oddly, this is may also be a picture of an introduction of sorts. Alt-right and #blacklivesmatter groups almost certainly interact significantly. In fact, it is doubtful that, even though they speak in a common language , one group can comprehend the other. The trajectories of their defining stories are so different, so misaligned, that the concepts of one slide off the brain of the other.

Within each group, it is a different story. Each group shares a common narrative, that is expressed in words, appearance, and belief. And within each group, there is discussion and consensus. These are the most extreme examples of the people that we see in the photo. I don’t see anyone else in the image wearing chains or openly carrying guns. The presence of these individuals within their respective groups exerts a pull on the overall orientation and position of the group in the things that they will accept. Additionally, the individuals in one group can cluster in opposition to a different group, which is a pressure that drives each group further apart.

Lastly, we come to the third actor in the image, the viewer. The photo is taken by Shelby Lum, an award-winning staff photographer for the Richmond Times-Dispatch. Through framing, focus and timing, she captures this frame that tells this story.  Looking at this photo, we the audience feel that we understand the situation. But photographs are inherently simplifying. The audience fills in the gaps – what’s happened before, the backstory of the people in the image. This image can mean many things to many people. And as such, it’s what we do with that photo – what we say about it and what we connect with it that makes the image as much about us as it is about the characters within the frame.

It is those interactions that I focus on, the ways that we as populations interact with information that supports, expands, or undermines our beliefs. My theory is that humans move through belief space like animals move on the planes of the Serengeti. And just as the status of the ecosystem can be inferred through the behaviors of its animal population, the health and status of our belief spaces can be determined by our digital behaviors.

Using this approach, I believe that we may be able look at populations at scale to determine the “health” of the underlying information. Wildebeest behave differently in risky environments. Their patterns of congregation are different. They can stampede, particularly when the terrain is against them, such as a narrow water crossing. Humans can behave in similar ways for example when their core beliefs about their identity is challenged, such as when Galileo was tried by the church for essentially moving man from the literal center of the universe..

I think that this sort of approach can be used to identify at-risk (stampeding) groups and provide avenues for intervention that can “nudge” groups off of dangerous trajectories. It may also be possible to recognize the presence of deliberate actors attempting to drive groups into dangerous terrain, like native Americans driving buffalo off of pishkun cliffs, or more recently the Russian Internet Research Agency instigating and coordinating a #bluelivesmatter and a #blacklivesmatter demonstration to occur at the same time and place in Texas.

This theory is based on simulations that are based on the assumption that people coordinate in high-dimensional belief spaces based on orientation, velocity and social influence. Rather than coming to a static consensus, these interactions are dynamic and follow intuitions of belief movement across information terrain. That dynamic process is what I’ll be discussing over the next several posts.

The Radio in Fascist Italy

The Radio in Fascist Italy

  • Philip Cannistraro
  • Journal of European Studies
  • scholars have generally agreed that the control of the mass media by the state is a fundamental prerequisite for the establishment and maintenance of totalitarian dictatorships (pg 127)
  • It is not so widely acknowledged, however, that contemporary totalitarian governments have been largely responsible for the initial growth of the mass media-particularly films and the radio-in their respective countries. (pg 127)
  • In their efforts to expose entire populations to official propaganda, totalitarian regimes encouraged and sponsored the development of the mass media and made them available to every· citizen on a large scale basis. (pg 127)
  • Marconi shrewdly reminded Mussolini that it would be politically wise to place control of the radio in the hands of the state, pointing out the radio’s great potential for propaganda purposes (pg 128)
  • “How many hearts recently beat with emotion when hearing the very voice of the Duce! All this means but one thing: the radio must be extended and extended rapidly. It will contribute much to the general culture of the people” (pg 129)
  • … to insure that EIAR’s programmes conformed to the requirements of the regime’s cultural and political policies. The High Commission included government representatives from each major area of culture: literature, journalism., the fine arts, music, poetry, theatre, and films. The programmes Commission screened the transcripts and plans of all and censored the content of all broadcasts. (pg 130)
  • His broadcast, ‘The Bombardment of Adrianople’, was awaited by the public with great interest and was heralded by critics as the most significant cultural event of the Italian radio.ts Marinetti’s colourful language and emotion-packed presentation blasted un expected life into the Italian radio. His flam.boyant style introduced the concept of the ‘radio personality’ in Fascist Italy, and the success of his talk encouraged those who, like Marinetti himself, hoped to make the radio a new art form. Broadcasts by Marinetti, most of which were lectures on Futurism, continued to be heard on Italian radio each month for more than a decade. (pg 131)
  • The regime quickly recognized the effectiveness of this technique in· arousing listener interest, and it was an easy matter to transfer microphones to mass rallies from where the enthusiastic cheers of the spectators could be heard by radio audiences. (pg 132)
  • The popular announcer Cesare Ferri created the characters ‘Nonno Radio’ (Grandfather Radio) and ‘Zia Radio’ (Aunt Radio), speaking to Italian youth with unprecedented familiarity in terms they easily understood. (pg 132)
  • In order to popular arouse interest in its program.me EIAR sought to stimulate indirect audience participation through public contests for short stories, poems, songs, In and children’s fairy tales. addition, surveys were conducted among listeners to discover trends in popular taste. (pg 133)
  • The radio had an important task to fulfil in the totalitarian state, that of binding the Italians together into one nation through common ideals and a common cultural experience inspired by Fascism. (pg 134)
  • Mussolini proclaimed Radio Rurale a great achievement of the Fascist revolution, for contemporary observers saw it as a new instrument with which to integrate rural existence into the mainstream. of national life. (pg 135)
  • The measures taken by the regime to overcome cultural and political provincialism by creating a mass radio audience in the countryside met with qualified success. (pg 137)
  • Regarded by many as an important step towards the creation of a truly popular culture, Radio Btdilla’s purpose was to give the working classes of the city and the countryside the means of acquiring a radio at a modest cost. Through the radio art, instruction, music, poetry-all the cultural masterworks–cease to become the privilege and unjust monopoly of a few elitist groups’. (pg 139)
  • ‘The ministry, in carrying out its delicate functions of vigilance over radio broadcasting, must guide itself by criteria that are essentially of a political and cultural nature.’ (pg 140)
  • Once the radio had been integrated into the structure of the Ministry of Popular Culture, the Fascists began to develop m.ore effective ways of using broadcasting as a cultural medium. While the number and variety of programmes had begun to increase by the beginning of the decade, it was only after 1934 that they became politically sophisticated. (pg 141)
  • Fascist racial doctrines became a major theme of radio propaganda during World War II. An Italo-German accord signed in 1940 to co-ordinate radio propaganda between the two countries included measures to ‘intensify anti-Jewish propaganda’ on the Italian radio as well as in foreign broadcasts.78 The Inspectorate for Radio Broadcasting organized an important series of anti-Semitic prograrnm.es that centred around the ‘Protocols of Zion’, and talks such as ‘Judaism. versus Western Culture’, the ‘Jewish International’, and ‘Judaism. Wanted this War’, were broadcast from 1941 to 1943. (pg 143)
  • information received from the Vatican radio during World War II was generally regarded more accurate than the obvious propaganda broadcasts of the Allies (pg 147)
  • On the radio he astutely employed direct, forceful language, shouting short and vivid sentences to create a sense of drama and arouse emotional reactions. ‘This ‘maniera forte’ that characterized Appelius’ radio talks had a great appeal for many Italians, especially for the ‘little man’ who wanted to be talked to on his own level in terms he could readily understand.121 In his broadcasts Appelius screamed insults and ranted and raved at the foul enemies of Fascism. with a powerful barrage of verbal abuse, inciting his audiences to unmitigated hatred and scorn against the evil ‘anglo-sassoni’ and their allies. (pg 150)
  • In the broad context of Fascist cultural aspirations, all the media aimed at similar goals: the diffusion of standard images and themes that reflected the ideological values of Fascism.; the creation of a mass culture that conformed the needs of the Fascist state in its capacity as a totalitarian to government. (pg 154)

Why Trump cooperates with Putin

Some thoughts about Trump’s press conference with Putin, as opposed to the G7 and NATO meetings, from a game-theoretic perspective. Yes, it’s time for some (more) game theory!

Consider the iterated prisoner’s dilemma (IPD), where two prisoners are being interrogated by the police. They have two choices: COOPERATE by remaining silent, or DEFECT by confessing. If both remain silent, they get a light punishment, since the police can’t prove anything. If one prisoner confesses while the other remains silent, the confessing prisoner goes free and the other faces the steepest punishment. If they both confess, they get a moderate punishment.

Axelrod, in The Evolution of Cooperation, shows that there are several strategies that one can use in the IPD and that these strategies vary by the amount of contact expected in the future. If none or very little future interaction is expected, then it pays to DEFECT, which basically means to screw your opponent.

If, on the other hand, there is an expectation of extensive future contact, the best strategy is some form of TIT-FOR-TAT, which means that you start by cooperating with your opponent, but if they defect, then you match that defection with their own. If they cooperate, then you match that as well.

This turns out to be a simple, clear strategy that rewards cooperative behavior and punishes jerks. It is powerful enough that a small cluster of TIT-FOR-TAT can invade a population of ALL_DEFECT. It has some weaknesses as well. We’ll get to that later.

Donald Trump, in the vast majority of his interactions has presented an ALL_DEFECT strategy. That actually can make sense in the world of real-estate, where there are lots of players that perform similar roles and bankruptcy protections exist. In other words, he could screw his banks, partners and contractors and get away with it, because there was always someone new.

But with Russia in general and Putin in particular, Trump is very cooperative. Why is this case different?

It turns out that  after four bankruptcies (1991, 1992, 2004 and 2009) it became impossible for Trump to get loans through traditional channels. In essence, he had defected on enough banks that the well was poisoned.

As the ability to get loans decreased, the amount of cash sales to Russian oligarchs increased. About $109 million were spent purchasing Trump-branded properties from 2003 – 2017, according to MccLatchy. Remember that TIT-FOR-TAT can win over ALL_DEFECT if there is prolonged interaction. Fourteen years is a long time to train someone.

Though TIT-FOR-TAT is effective, it’s hard work trying to figure out what the other player is likely to do. TIT-FOR-TAT’s weakness is its difficulty. We simply can’t do Nash equilibria in our heads. However, there are two cognitively easy strategies in the IPD: ALL_DEFECT, and ALL_COOPERATE. Trump doesn’t like to work hard, and he doesn’t listen to staff, so I think that once Trump tried DEFECT a few times and got punished for it he went for ALL_COOPERATE with the Russians. My guess is that they have a whole team of people working on how to keep him there. They do the work so he doesn’t have to think about it.

Which is why, at every turn, Trump cooperates. He knows what will happen if he doesn’t, and frankly, it’s less work than any of the other alternatives. And if you really only care for yourself, that’s a perfectly reasonable place to be.

Postscript – July 18, 2018

I’ve had some discussions about this where folks are saying “That’s too much analysis for this guy. He’s just an idiot who likes strongmen”. But here’s the thing. It’s not about Trump. It’s about Putin.

What do you think the odds were on Trump winning the election in 2015? Now how about 2003, when he started getting Russian cash to prop up his businesses? For $110M, or the price of ONE equipped F/A-18, amortized over 14 years, they were able to secure the near total cooperation of a low-likelihood presidential contender/disruptor and surprise winner.

This is a technique that the Russians have developed and refined for years. So you have to start asking the questions about other individuals and groups that are oddly aligned with Putin’s aims. Russia has a budget that could support thousands of “investments” like Trump, here and abroad.

That’s the key. And that’s my bet on why Mueller is so focused on finances. The Russians learned an important lesson in spending on weapons in the Reagan administration. They can’t compete on the level of spending. So it appears that they might be allocating resources towards low-cost social weaponry to augment their physical capabilities. If you want more on this, read Gerasimov’s The value of Science is in the Foresight.

Postscript 2 – July 21, 2018

A paragraph from a the very interesting New Yorker article by Adam Davidson:

“Ledeneva told me that each actor in sistema faces near-constant uncertainty about his status, aware that others could well destroy him. Each actor also knows how to use kompromat to destroy rivals but fears that using such material might provoke an explosive response. While each person in sistema feels near-constant uncertainty, the over-all sistema is remarkably robust. Kompromat is most powerful when it isn’t used, and when its targets aren’t quite clear about how much destructive information there is out there. If everyone sees potential land mines everywhere, it dramatically increases the price for anybody stepping out of line.”

It’s an interesting further twist on the ALL_COOPERATE. One of the advantages of nuclear MAD was that it was simple. That it could also apply to more mundane blackmail shouldn’t be surprising.

From I to We: Group Formation and Linguistic Adaption in an Online Xenophobic Forum

From I to We: Group Formation and Linguistic Adaption in an Online Xenophobic Forum

Authors

Venue: Journal of Social and Political Psychology

Quick takeaway:

  • Linguistic study of a xenophobic online chat room using Pennebaker’s LIWC text analytic system. Users who stay in the group change from individual to group pronouns and align linguistically. Cognitive complexity also appears to reduce as users align with the group

Abstract:

  • Much of identity formation processes nowadays takes place online, indicating that intergroup differentiation may be found in online communities. This paper focuses on identity formation processes in an open online xenophobic, anti-immigrant, discussion forum. Open discussion forums provide an excellent opportunity to investigate open interactions that may reveal how identity is formed and how individual users are influenced by other users. Using computational text analysis and Linguistic Inquiry Word Count (LIWC), our results show that new users change from an individual identification to a group identification over time as indicated by a decrease in the use of “I” and increase in the use of “we”. The analyses also show increased use of “they” indicating intergroup differentiation. Moreover, the linguistic style of new users became more similar to that of the overall forum over time. Further, the emotional content decreased over time. The results indicate that new users on a forum create a collective identity with the other users and adapt to them linguistically.

Notes:

  • Social influence is broadly defined as any change – emotional, behavioral, or attitudinal – that has its roots in others’ real or imagined presence (Allport, 1954). (pg 77)
  • Regardless of why an individual displays an observable behavioral change that is in line with group norms, social identification with a group is the basis for the change. (pg 77)
  • In social psychological terms, a group is defined as more than two people that share certain goals (Cartwright & Zander, 1968). (pg 77)
  • Processes of social identification, intergroup differentiation and social influence have to date not been studied in online forums. The aim of the present research is to fill this gap and provide information on how such processes can be studied through language used on the forum. (pg 78)
  • The popularity of social networking sites has increased immensely during the last decade. At the same time, offline socializing has shown a decline (Duggan & Smith, 2013). Now, much of the socializing actually takes place online (Ganda, 2014). In order to be part of an online community, the individual must socialize with other users. Through such socializing, individuals create self-representations (Enli & Thumim, 2012). Hence, the processes of identity formation, may to a large extent take place on the Internet in various online forums. (pg 78)
  • For instance, linguistic analyses of American Nazis have shown that use of third person plural pronouns (they, them, their) is the single best predictor of extreme attitudes (Pennebaker & Chung, 2008). (pg 79)
  • Because language can be seen as behavior (Fiedler, 2008), it may be possible to study processes of social influence through linguistic analysis. Thus, our second hypothesis is that the linguistic style of new users will become increasingly similar to the linguistic style of the overall forum over time (H2). (pg 79)
  • This indicates that the content of the posts in an online forum may also change over time as arguments become more fine-tuned and input from both supporting and contradicting members are integrated into an individual’s own beliefs. This is likely to result (linguistically) in an increase in indicators of cognitive complexity. Hence, we hypothesize that the content of the posts will change over time, such that indicators of complex thinking will increase (H3a). (pg 80)
    • I’m not sure what to think about this. I expect from dimension reduction, that as the group becomes more aligned, the overall complex thinking will reduce, and the outliers will leave, at least in the extreme of a stampede condition.
  • This result indicates that after having expressed negativity in the forum, the need for such expressions should decrease. Hence, we expect that the content of the posts will change such that indicators of negative emotions will decrease, over time (H3b). (pg 80)
  • the forum is presented as a “very liberal forum”, where people are able to express their opinions, whatever they may be. This “extreme liberal” idea implies that there is very little censorship the forum is presented as a “very liberal forum”, where people are able to express their opinions, whatever they may be. This “extreme liberal” idea implies that there is very little censorship, which has resulted in that the forum is highly xenophobic. Nonetheless, due to its liberal self-presentation, the xenophobic discussions are not unchallenged. For example, also anti-racist people join this forum in order to challenge individuals with xenophobic attitudes. This means that the forum is not likely to function as a pure echo chamber, because contradicting arguments must be met with own arguments. Hence, individuals will learn from more experienced users how to counter contradicting arguments in a convincing way. Hence, they are likely to incorporate new knowledge, embrace input and contribute to evolving ideas and arguments. (pg 81)
    • Open debate can lead to the highest level of polarization (M&D)
    • There isn’t diverse opinion. The conversation is polarized, with opponents pushing towards the opposite pole. The question I’d like to see answered is has extremism increased in the forum?
  • Natural language analyses of anonymous social media forums also circumvent social desirability biases that may be present in traditional self-rating research, which is a particular important concern in relation to issues related to outgroups (Maass, Salvi, Arcuri, & Semin, 1989; von Hippel, Sekaquaptewa, & Vargas, 1997, 2008). The to-be analyzed media uses “aliases”, yielding anonymity of the users and at the same time allow us to track individuals over time and analyze changes in communication patterns. (pg 81)
    • After seeing “Ready Player One”, I also wonder if the aliases themselves could be looked at using an embedding space built from the terms used by the users? Then you get distance measurements, t-sne projections, etc.
  • Linguistic Inquiry Word Count (LIWC; Pennebaker et al., 2007; Chung & Pennebaker, 2007; Pennebaker, 2011b; Pennebaker, Francis, & Booth, 2001) is a computerized text analysis program that computes a LIWC score, i.e., the percentage of various language categories relative to the number of total words (see also www.liwc.net). (pg 81)
    • LIWC2015 ($90) is the gold standard in computerized text analysis. Learn how the words we use in everyday language reveal our thoughts, feelings, personality, and motivations. Based on years of scientific research, LIWC2015 is more accurate, easier to use, and provides a broader range of social and psychological insights compared to earlier LIWC versions
  • Figure 1c shows words overrepresented in later posts, i.e. words where the usage of the words correlates positively with how long the users has been active on the forum. The words here typically lack emotional content and are indicators of higher complexity in language. Again, this analysis provides preliminary support for the idea that time on the forum is related to more complex thinking, and less emotionality.
    • WordCloud
  • The second hypothesis was that the linguistic style of new users would become increasingly similar to other users on the forum over time. This hypothesis is evaluated by first z-transforming each LIWC score, so that each has a mean value of zero and a standard deviation of one. Then we measure how each post differs from the standardized values by summing the absolute z-values over all 62 LIWC categories from 2007. Thus, low values on these deviation scores indicate that posts are more prototypical, or highly similar, to what other users write. These deviation scores are analyzed in the same way as for Hypothesis 1 (i.e., by correlating each user score with the number of days on the forum, and then t-testing whether the correlations are significantly different from zero). In support of the hypothesis, the results show an increase in similarity, as indicated by decreasing deviation scores (Figure 2). The mean correlation coefficient between this measure and time on the forum was -.0086, which is significant, t(11749) = -3.77, p < 0.001. (pg 85)
    • ForumAlignmentI think it is reasonable to consider this a measure of alignment
  • Because individuals form identities online and because we see this in the use of pronouns, we also expected to see tendencies of social influence and adaption. This effect was also found, such that individuals’ linguistic style became increasingly similar to other users’ linguistic style over time. Past research has shown that accommodation of communication style occurs automatically when people connect to people or groups they like (Giles & Ogay 2007; Ireland et al., 2011), but also that similarity in communicative style functions as cohesive glue within a group (Reid, Giles, & Harwood, 2005). (pg 86)
  • Still, the results could not confirm an increase in cognitive complexity. It is difficult to determine why this was not observed even though a general trend to conform to the linguistic style on the forum was observed. (pg 87)
    • This is what I would expect. As alignment increases, complexity, as expressed by higher dimensional thinking should decrease.
  • This idea would also be in line with previous research that has shown that expressing oneself decreases arousal (Garcia et al., 2016). Moreover, because the forum is not explicitly racist, individuals may have simply adapted to the social norms on the forum prescribing less negative emotional displays. Finally, a possible explanation for the decrease in negative emotional words might be that users who are very angry leave the forum, because of its non-racist focus, and end up in more hostile forums. An interesting finding that was not part of the hypotheses in the present research is that the third person plural category correlated positively with all four negative emotions categories, suggesting that people using for example ‘they’ express more negative emotions (pg 87)
  • In line with social identity theory (Tajfel & Turner, 1986), we also observe linguistic adaption to the group. Hence, our results indicate that processes of identity formation may take place online. (pg 87)

Influence of augmented humans in online interactions during voting events

Influence of augmented humans in online interactions during voting events

  • Massimo Stella (Scholar)
  • Marco Cristoforetti (Scholar)
  • Marco Cristoforetti (Scholar)
  • Abstract: Overwhelming empirical evidence has shown that online social dynamics mirrors real-world events. Hence, understanding the mechanisms leading to social contagion in online ecosystems is fundamental for predicting, and even manouvering, human behavior. It has been shown that one of such mechanisms is based on fabricating armies of automated agents that are known as social bots. Using the recent Italian elections as an emblematic case study, here we provide evidence for the existence of a special class of highly influential users, that we name “augmented humans”. They exploit bots for enhancing both their visibility and influence, generating deep information cascades to the same extent of news media and other broadcasters. Augmented humans uniformly infiltrate across the full range of identified clusters of accounts, the latter reflecting political parties and their electoral ranks.
  • Bruter and Harrison [19] shift the focus on the psychological in uence that electoral arrangements exert on voters by altering their emotions and behavior. The investigation of voting from a cognitive perspective leads to the concept of electoral ergonomics: Understanding optimal ways in which voters emotionally cope with voting decisions and outcomes leads to a better prediction of the elections. (pg 1)
  • Most of the Twitter interactions are from humans to bots (46%); Humans tend to interact with bots in 56% of mentions, 41% of replies and 43% of retweets. Bots interact with humans roughly in 4% of the interactions, independently on interaction type. This indicates that bots play a passive role in the network but are rather highly mentioned/replied/retweeted by humans. (pg 2)
  • bots’ locations are distributed worldwide and they are present in areas where no human users are geo-localized such as Morocco.  (pg 2)
  • Since the number of social interactions (i.e., the degree) of a given user is an important estimator of the in uence of user itself in online social networks [1722], we consider a null model fixing users’ degree while randomizing their connections, also known as configuration model [2324].  (pg 2)
  • During the whole period, bot bot interactions are more likely than random (Δ > 0), indicating that bots tend to interact more with other bots rather than with humans (Δ < 0) during Italian elections. Since interactions often encode the spread of a given content online [16], the positive assortativity highlights that bots share contents mainly with each other and hence can resonate with the same content, be it news or spam.  (pg 2)
  • Differently from previous works, where the semantic content of bots and humans differs in its emotional polarity [12], in here we nd that bots mainly repeat the same political content of human users, thus boosting the spreading of hashtags strongly related to the electoral process, such as hashtags referring to the government or to political victory, names of political parties or names of influential politicians (see also 3). (pg 4)
  • Frequencies of individual hashtags during the whole electoral process display some interesting shifts, reported in Table III (Top). For instance, the hashtag #exitpoll, indicating the electoral outcome, becomes 10000 times more frequent on the voting day than before March 4. These shifts indicate that the frequency of hashtags reflects real-world events, thus underlining the strong link between online social dynamics and the real-world electoral process. (pg 4)
  • TABLE II. Top influencers are mostly bots. Hubs characterize influential users and broadcasters in online social systems [17], hence we use degree rankings for identifying the most in uential users in the network. (pg 5)
  • bots are mostly influential nodes which tend to interact mostly with other bots rather than humans and, when they interact with human users, they preferentially target the most influential ones. (pg 5)
  • we first filter the network by considering only pair of users with at least one retweet, with either direction, because re-sharing content it is often a good proxy of social endorsement [21]. However, Retweets alone are not sufficient to wash out the noise intrinsic to systems like Twitter, therefore we apply a more selective restriction, by requiring that at least another social action – i.e., either mention or reply – must be present in addition to a retweet [12]. This restrictive selection allows one to filter out all spurious interactions among users with the advantage of not requiring any thresholding approach with respect to the frequency of interactions themselves. (pg 5)
  • The resulting network is what we call the social bulk, i.e. a network core of endorsement and exchange among users. By construction, information ows among users who share strong social relationships and are characterized by similar ideologies: in fact, when a retweet goes from one user to another one, both of them are endorsing the same content, thus making non-directionality a viable approach for representing the endorsement related to content sharing. (pg 5)
  • Fiedler partitioning
  • The relevant literature has used the term “cyborg” for identifying indistinctly bot-assisted human or human-assisted bot accounts generating spam content over social platforms such as Twitter [5, 35]. Here, we prefer to use the term \augmented human” for indicating specifically those human accounts exploiting bots for artificially increasing, i.e. augmenting, their in uence in online social platforms, analogously to physical augmentation improving human performances in the real world [36]. (pg 8)
  • Baseline social behavior is defined by the medians of the two observables, like shown in Fig. 6c. This map allows to easily identify four categories of individuals in the social dynamics: i) hidden in uentials, generating information cascades rapidly spreading from a large small number of followers; ii) in uentials, generating information cascades rapidly spreading from a large number of followers; iii) broadcasters, generating information cascades slowly spreading from a large number of followers; iv) common users, generating information cascades slowly spreading from a small number of followers. (pg 9)
  • Hidden influentials, known to be efficient spreaders in viral phenomena [45], are mostly humans: in this category falls the augmented humans, assisted by social bots to increase their online visibility. (pg 10)
  • We define augmented humans as human users having at least 50% + 1 of bot neighbours in the social bulk. We discard users having less than 3 interactions in the social bulk. (pg 10)
  • The most central augmented human in terms of number of social interactions is Utente01, which interacts with 2700 bots and 55 humans in the social bulk. (pg 10)
  • The above cascade analysis reveals that almost 2 out 3 augmented humans resulted playing an important role in the flow of online content: 67% of augmented humans were either influentials or hidden influentials or broadcasters. These results strongly support the idea that via augmentation even common users can become social influencers without having a large number of followers/friends but rather by recurring to the aid of either armies of bots (e.g., Utente01, an hidden in uential) or the selection of a few key helping bots. (pg 11)

Consensus and Cooperation in Networked Multi-Agent Systems

Consensus and Cooperation in Networked Multi-Agent Systems

Journal: Proceedings of the IEEE

  • Proceedings of the IEEE is the leading journal to provide an in-depth review, survey, and tutorial coverage of the technical developments in electronics, electrical and computer engineering, and computer science. Consistently ranked as one of the top journals by Impact Factor, Article Influence Score and more, the journal serves as a trusted resource for engineers around the world

Authors:

Abstract:

  • This paper provides a theoretical framework for analysis of consensus algorithms for multi-agent networked systems with an emphasis on the role of directed information flow, robustness to changes in network topology due to link/node failures, time-delays, and performance guarantees. An overview of basic concepts of information consensus in networks and methods of convergence and performance analysis for the algorithms are provided. Our analysis framework is based on tools from matrix theory, algebraic graph theory, and control theory. We discuss the connections between consensus problems in networked dynamic systems and diverse applications including synchronization of coupled oscillators, flocking, formation control, fast consensus in small world networks, Markov processes and gossip-based algorithms, load balancing in networks, rendezvous in space, distributed sensor fusion in sensor networks, and belief propagation. We establish direct connections between spectral and structural properties of complex networks and the speed of information diffusion of consensus algorithms. A brief introduction is provided on networked systems with non-local information flow that are considerably faster than distributed systems with lattice-type nearest neighbor interactions. Simulation results are presented that demonstrate the role of small world effects on the speed of consensus algorithms and cooperative control of multi vehicle formations.

Notes:

  • In networks of agents (or dynamic systems), “consensus” means to reach an agreement regarding a certain quantity of interest that depends on the state of all agents. A “consensus algorithm” (or protocol) is an interaction rule that specifies the information exchange between an agent and all of its (nearest) neighbors on the network (pp 215)
    • In my work, this is agreement on heading and velocity
  • Graph Laplacians are an important point of focus of this paper. It is worth mentioning that the second smallest eigenvalue of graph Laplacians called algebraic connectivity quantifies the speed of convergence of consensus algorithms. (pp 216)
  • More recently, there has been a tremendous surge of interest among researchers from various disciplines of engineering and science in problems related to multi-agent networked systems with close ties to consensus problems. This includes subjects such as consensus [26]–[32], collective behavior of flocks and swarms [19], [33]–[37], sensor fusion [38]–[40], random networks [41], [42], synchronization of coupled oscillators [42]–[46], algebraic connectivity of complex networks [47]–[49], asynchronous distributed algorithms [30], [50], formation control for multi-robot systems [51]–[59], optimization-based cooperative control [60]–[63], dynamic graphs [64]–[67], complexity of coordinated tasks [68]–[71], and consensus-based belief propagation in Bayesian networks [72], [73]. (pp 216)
    • That is a dense lit review. How did they order it thematically?
  • A byproduct of this framework is to demonstrate that seemingly different consensus algorithms in the literature [10], [12]–[15] are closely related. (pp 216)
  • To understand the role of cooperation in performing coordinated tasks, we need to distinguish between unconstrained and constrained consensus problems. An unconstrained consensus problem is simply the alignment problem in which it suffices that the state of all agents asymptotically be the same. In contrast, in distributed computation of a function f(z), the state of all agents has to asymptotically become equal to f(z), meaning that the consensus problem is constrained. We refer to this constrained consensus problem as the f-consensus problem. (pp 217)
    • Normal exploring/flocking/stampeding is unconstrained. Herding adds constraint, though it’s dynamic. The variables that have to be manipulated in the case of constraint to result in the same amount of consensus are probably what’s interesting here. Examples could be how ‘loud’ does the herder have to be? Also, how ‘primed’ does the population have to be to accept herding?
  • …cooperation can be informally interpreted as “giving consent to providing one’s state and following a common protocol that serves the group objective.” (pp 217)
  • Formal analysis of the behavior of systems that involve more than one type of agent is more complicated, particularly, in presence of adversarial agents in noncooperative games [79], [80]. (pp 217)
  • The reason matrix theory [81] is so widely used in analysis of consensus algorithms [10], [12], [13], [14], [15], [64] is primarily due to the structure of P in (4) and its connection to graphs. (pp 218)
  • The role of consensus algorithms in particle based flocking is for an agent to achieve velocity matching with respect to its neighbors. In [19], it is demonstrated that flocks are networks of dynamic systems with a dynamic topology. This topology is a proximity graph that depends on the state of all agents and is determined locally for each agent, i.e., the topology of flocks is a state dependent graph. The notion of state-dependent graphs was introduced by Mesbahi [64] in a context that is independent of flocking. (pp 218)
    • They leave out heading alignment here. Deliberate? Or is heading alignment just another variant on velocity
  • Consider a network of decision-making agents with dynamics ẋi = ui interested in reaching a consensus via local communication with their neighbors on a graph G = (V, E). By reaching a consensus, we mean asymptotically converging to a one-dimensional agreement space characterized by the following equation: x1 = x2 = … = x (pp 219)
  • A dynamic graph G(t) = (V, E(t)) is a graph in which the set of edges E(t) and the adjacency matrix A(t) are time-varying. Clearly, the set of neighbors Ni(t) of every agent in a dynamic graph is a time-varying set as well. Dynamic graphs are useful for describing the network topology of mobile sensor networks and flocks [19]. (pp 219)
  • GraphLaplacianGradientDescent(pp 220)
  • algebraic connectivity of a graph: The algebraic connectivity (also known as Fiedler value or Fiedler eigenvalue) of a graph G is the second-smallest eigenvalue of the Laplacian matrix of G.[1] This eigenvalue is greater than 0 if and only if G is a connected graph. This is a corollary to the fact that the number of times 0 appears as an eigenvalue in the Laplacian is the number of connected components in the graph. The magnitude of this value reflects how well connected the overall graph is. It has been used in analysing the robustness and synchronizability of networks. (wikipedia) (pp 220)
  • According to Gershgorin theorem [81], all eigenvalues of L in the complex plane are located in a closed disk centered at delta + 0j with a radius of delta, the maximum degree of a graph (pp 220)
    • This is another measure that I can do of the nomad/flock/stampede structures combined with DBSCAN. Each agent knows what agents it is connected with, and we know how many agents there are. Each agent row should just have the number of agents it is connected to.
  • In many scenarios, networked systems can possess a dynamic topology that is time-varying due to node and link failures/creations, packet-loss [40], [98], asynchronous consensus [41], state-dependence [64], formation reconfiguration [53], evolution [96], and flocking [19], [99]. Networked systems with a dynamic topology are commonly known as switching networks. (pp 226)
  • Conclusion: A theoretical framework was provided for analysis of consensus algorithms for networked multi-agent systems with fixed or dynamic topology and directed information flow. The connections between consensus problems and several applications were discussed that include synchronization of coupled oscillators, flocking, formation control, fast consensus in small-world networks, Markov processes and gossip-based algorithms, load balancing in networks, rendezvous in space, distributed sensor fusion in sensor networks, and belief propagation. The role of “cooperation” in distributed coordination of networked autonomous systems was clarified and the effects of lack of cooperation was demonstrated by an example. It was demonstrated that notions such as graph Laplacians, nonnegative stochasticmatrices, and algebraic connectivity of graphs and digraphs play an instrumental role in analysis of consensus algorithms. We proved that algorithms introduced by Jadbabaie et al. and Fax and Murray are identical for graphs with n self-loops and are both special cases of the consensus algorithm of Olfati-Saber and Murray. The notion of Perron matrices was introduced as the discrete-time counterpart of graph Laplacians in consensus protocols. A number of fundamental spectral properties of Perron matrices were proved. This led to a unified framework for expression and analysis of consensus algorithms in both continuous-time and discrete-time. Simulation results for reaching a consensus in small-worlds versus lattice-type nearest-neighbor graphs and cooperative control of multivehicle formations were presented. (pp 231)