diff --git a/assets/img/decision_model_1.png b/assets/img/decision_model_1.png new file mode 100644 index 0000000..3f8a3a0 Binary files /dev/null and b/assets/img/decision_model_1.png differ diff --git a/assets/img/decision_model_2.png b/assets/img/decision_model_2.png new file mode 100644 index 0000000..387ba91 Binary files /dev/null and b/assets/img/decision_model_2.png differ diff --git a/assets/img/decision_model_3.png b/assets/img/decision_model_3.png new file mode 100644 index 0000000..32ca4f8 Binary files /dev/null and b/assets/img/decision_model_3.png differ diff --git a/assets/img/decision_model_4.png b/assets/img/decision_model_4.png new file mode 100644 index 0000000..6a0bcc6 Binary files /dev/null and b/assets/img/decision_model_4.png differ diff --git a/index.md b/index.md index df8eb49..6eee64c 100755 --- a/index.md +++ b/index.md @@ -22,7 +22,7 @@ Starting with the Fall 2019 offering of CS 224W, the course covers three broad t 3. [Influence Maximization](): Influential sets, submodularity, hill climbing 4. [Outbreak Detection](): CELF, lazy hill climbing 5. [Link Analysis](): PageRank and SimRank -6. [Network Effects and Cascading Behavior](): Decision-based diffusion, probabilistic contagion, SEIZ +6. [Network Effects and Cascading Behavior](network-methods/network-effects-and-cascading-behavior): Decision-based diffusion, probabilistic contagion, SEIZ 7. [Network Robustness](): Power laws, preferential attachment 8. [Network Evolution](): Densification, forest fire, temporal networks with PageRank 9. [Knowledge Graphs and Metapaths](): Metapaths, reasoning and completion of KGs diff --git a/network-methods/network-effects-and-cascading-behavior.md b/network-methods/network-effects-and-cascading-behavior.md new file mode 100644 index 0000000..09fb85a --- /dev/null +++ b/network-methods/network-effects-and-cascading-behavior.md @@ -0,0 +1,62 @@ +--- +layout: post +title: Network Effects And Cascading Behaviour +header-includes: + - \usepackage{amsmath} +--- + +In this section, we study how a infection propages through a network. We will look into two classed of model, namely decision based models and probabilistic models. But first lets look at some terminology used throughout the post. + +**Terminology** +1. Cascade: Propagation tree created by spreading contagion +2. Contagion: What is spreading in the network, e.g., diseases, tweet, etc. +3. Infection: Adoption/activation of a node +4. Main players: Infected/active nodes, early adopters + +# Decision Based Models +In decision based models, every nodes independently decides whether to adopt the contagion or not depending upon its neighbors. The decision is modelled as a two-player coordination game between user and its neighbor and related payoffs. Hence a node with degree $$k$$ plays $$k$$ such games to decide its payoff and correspondingly its behavior. + +## Single Contagion Model +There are two contagions $$A$$ and $$B$$ in the network and initially every node has behavior $$B$$. Every node can have only one behavior out of the two. The payoff matrix is given as: + +| | A | B | +|---|---|---| +| A | a | 0 | +| B | 0 | b | + +Lets analyze a node with d neighbors, and let p be the fraction of nodes who have adopted $$A$$. Hence the payoff for $$A$$ is $$apd$$ and payoff for $$B$$ is $$b(1-p)d$$. Hence the node adopts behavior $$A$$ if +$$apd > b(1-p)d \implies p > \frac{b}{a+b} = q$$(threshold) + +### Case Study: [Modelling Protest Recruitment on social networks](https://arxiv.org/abs/1111.5595) +Key Insights: +- Uniform activation threhold for users, with two peaks +- Most cascades are short +- Successful cascades are started by central users + +#### Note: +**k-core decomposition**: biggest connected subgraph where every node has at least degree k (iteratively remove nodes with degree less than k) + +### Multiple Contagion Model +There are two contagions $$A$$ and $$B$$ in the network and initially every node has behavior $$B$$. In this case a node can have both behavior $$A$$ and $$B$$ at a total cost of $$c$$ (over all interactions). The payoff matrix is given as: + +| | A | B | AB | +|---|---|---|----| +| A | a | 0 | a | +| B | 0 | b | b | +| AB| a | b | max(a,b)| + +### Example: Infinite Line graph +**Case 1**:**A-w-B** +![decision_case_1](../assets/img/decision_model_1.png?style=centerme) + +Payoffs for $$w$$: $$A: a$$, $$B: 1$$, $$AB: a+1-c$$ + +![decision_case_2](../assets/img/decision_model_2.png?style=centerme) + +**Case 1**: **AB-w-B** +![decision_case_3](../assets/img/decision_model_3.png?style=centerme) + +Payoffs for $$w$$: $$A: a$$, $$B: 1$$, $$AB: max(a, 1) + 1 -c$$ + +![decision_case_4](../assets/img/decision_model_4.png?style=centerme) +