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Percolation threshold is a mathematical concept related to percolation theory, which is the formation of long-range connectivity in random systems. Below the threshold a giant connected component does not exist; while above it, there exists a giant component of the order of system size.

How can we calculate a percolation threshold of a graph/network using Mathematica?

  1. Image of a subcellular network: enter image description here

  2. The image is transformed into a graph by utilizing MorphologicalGraph function: enter image description here

  3. By applying the ConnectedComponents function and choosing the list of subgraphs from the suggestion menu one can obtain a soup of graphs/networks. Here are the top of that list: enter image description here

The question is how to exctract the probability that these networks are being connected? What is the critical treshold or bond percolation?

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  • $\begingroup$ demonstrations.wolfram.com/PercolationOnASquareGrid $\endgroup$
    – Feyre
    Commented Nov 4, 2016 at 22:20
  • $\begingroup$ This Q&A might also be of interest. $\endgroup$
    – march
    Commented Nov 4, 2016 at 22:25
  • $\begingroup$ @Feyre. Thank you so much. $\endgroup$ Commented Nov 5, 2016 at 0:01
  • $\begingroup$ i don't follow the probabilistic nature of the question. If you have many such images you could see how many show long range connectivity. Otherwise its not clear what you are asking. $\endgroup$
    – george2079
    Commented Nov 6, 2016 at 19:26
  • $\begingroup$ @george2079.Thank you for your consideration. I actually found this nice paper of Prof Oliver Knill "MATHEMATICA ROUTINES FOR INDEX EXPECTATION AND PERCOLATION " which kind of address the challenges I am dealing with at this point. Would appreciate any comments about what the code given actually does to define the site and bond percolations. $\endgroup$ Commented Nov 6, 2016 at 19:53

1 Answer 1

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Start with a symmetric matrix of random positive weights.

mybasicweightmatrix = (temp = Table[RandomReal[], {10}, {10}]) + 
   Transpose[temp]; (* symmetric matrix of random positive weights *)

Then threshold the entries such that values less than mythreshold will be set to $0$ (not connected), others to $1$ (connected). Form a graph based on this thresholded adjacency matrix. Then adjust mythreshold until the graph is no longer weakly connected.

Manipulate[
 thresholdedmatrix = (HeavisideTheta[# - mythreshold] & /@ 
    mybasicweightmatrix);

 myfig = Column[{mythreshold, 
    WeaklyConnectedGraphQ[nn = AdjacencyGraph[thresholdedmatrix]], 
    Graph[nn, GraphLayout -> "CircularEmbedding"]}],

 {mythreshold, 0, 2}]

Here "weakly connected" means there is a path from any vertex to any other vertex. Seems like a reasonable specification of a "giant component."

enter image description here

enter image description here

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  • $\begingroup$ G.Stork. Thank you very much. I am a neophyte to programming in general and WL in particular. Do you mind please describing what the code actually does. I am very appreciative. $\endgroup$ Commented Nov 5, 2016 at 0:04
  • $\begingroup$ @ G.Stork. Many Thanks! $\endgroup$ Commented Nov 5, 2016 at 1:20
  • $\begingroup$ Pure Function: You're welcome. Will you be using this in some publication or research? $\endgroup$ Commented Nov 5, 2016 at 4:47

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