What is the probability that a subgraph of a connected graph is also connected?

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Discussion Overview

The discussion revolves around the probability that a subgraph of a connected graph remains connected, particularly in the context of random graphs defined by parameters such as the number of nodes and edge probabilities. Participants explore the implications of different types of graphs and the criteria for selecting subgraphs.

Discussion Character

  • Exploratory, Technical explanation, Debate/contested

Main Points Raised

  • Samir initially asks for the probability that a subgraph of a connected graph is also connected, given a probability p that the graph is connected.
  • One participant argues that the answer depends heavily on the type of original graph, providing the example of a star graph where any subgraph must be connected.
  • Samir refines the question to focus on a random graph G(n,p) and asks about the probability of connectivity for a subgraph defined by nodes at a specific distance from a fixed node, questioning whether this probability is less than p and by how much.
  • Another participant comments on the introduction of the concept of distance, suggesting that if the fixed node is included in the subgraph, the subgraph must be connected based on the definition of distance.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the original question, as the discussion highlights differing views on the impact of graph structure on subgraph connectivity. There are competing perspectives on how to approach the problem based on the type of graph and the criteria for subgraph selection.

Contextual Notes

The discussion reveals limitations in the clarity of the original question and the assumptions about graph types and properties. The implications of distance in defining subgraphs are also noted but remain unresolved.

samirg
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Hi Guys
I need some help on graph connectivity problem.
Given a graph is connected with probability p, what is the probability that its subgraph is also connected?
In other words, we have to find the probability that a subgraph of a connected graph is connected?

I hope i have made my question clear. Any help in this matter is really appreciated.

Thanks

Samir
 
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It is impossible to answer the question without you saying more about the original graph. Given a "star graph" ie one central node and all vertices rays from it, then any subgraph must be connected, given another graph this will almost certainly fail to be true.
 
connectivity of graph(problem redefinition)

matt grime said:
It is impossible to answer the question without you saying more about the original graph. Given a "star graph" ie one central node and all vertices rays from it, then any subgraph must be connected, given another graph this will almost certainly fail to be true.

Hi matt

The problem can be stated as
Given a random graph G(n,p) where n is number of nodes in the graph and p is the probability that an edge exits between two nodes, (when p=0 graph does not have any edges and when p = 1 graph is fully connected.) then if i take a subgraph of this random graph based on criteria that all the nodes of this subgraph are at a particular distance from one fixed node, then what is the probability that this subgraph is connected? I want to know whether this probability will be less than p, and if yes how much less?

I hope this makes question a bit clearer.

Thanks again

Samir
 
Double and triple posting is generally frowned upon.

Now you've introduced the word distance. the usual distance on graph is the length of the shortest path between nodes, which when defined explicitly tells you the subgraph you've picked must be connected (assuming the fixed node is in the subgraph).
 

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