74 lines
2.1 KiB
Matlab
74 lines
2.1 KiB
Matlab
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% Degree-preserving rewiring of a given edge.
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% Note 1: Assume unweighted undirected graph.
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%
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% INPUTS: edge list, el (mx3) and the two nodes of the edge to be rewired.
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% OUTPUTS: rewired edge list, same size and same degree distribution
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%
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% Note: There are cases when rewiring is not possible with simultaneously
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% keeping the graph simple. Then an empty edge list is returned.
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%
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% Other routines used: edgeL2adj.m, kneighbors.m
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% GB: last updated, Oct 25, 2012
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function el = rewireThisEdge(el,i1,i2)
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% check whether the edge can actually be rewired ..................
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adj = edgeL2adj(el);
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neighbors = [i1, i2];
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neighbors = [neighbors kneighbors(adj,i1,1)];
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neighbors = [neighbors kneighbors(adj,i2,1)];
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disjoint_edges = [];
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for e=1:length(el)
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if sum(ismember(neighbors,el(e,1)))==0 && sum(ismember(neighbors,el(e,2)))==0
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disjoint_edges = [disjoint_edges; el(e,:)];
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end
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end
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if isempty(disjoint_edges)
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printf('rewireThisEdge(): cannot rewire this graph without adding a double edge or a loop\n');
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el = [];
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return
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end
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% .................................................................
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[~,row] = ismember([i1 i2 1],el,'rows');
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ind = [row];
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edge1=el(ind(1),:);
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% pick a random second edge from the disjoint edges
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randind = randi([1,size(disjoint_edges,1)]);
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edge2=disjoint_edges(randind,:);
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[~,ind2] = ismember([edge2(1) edge2(2) 1],el,'rows');
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ind = [ind ind2];
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if rand<0.5
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% first possibility: (e11,e22) & (e12,e21)
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el(ind(1),:)=[edge1(1),edge2(2),1];
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el(ind(2),:)=[edge1(2),edge2(1),1];
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% add the symmetric equivalents
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[~,inds1] = ismember([edge1(2),edge1(1),1],el,'rows');
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el(inds1,:)=[edge2(2),edge1(1),1];
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[~,inds2] = ismember([edge2(2),edge2(1),1],el,'rows');
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el(inds2,:)=[edge2(1),edge1(2),1];
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else
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% second possibility: (e11,e21) & (e12,e22)
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el(ind(1),:)=[edge1(1),edge2(1),1];
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el(ind(2),:)=[edge1(2),edge2(2),1];
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% add the symmetric equivalents
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[~,inds1] = ismember([edge1(2),edge1(1),1],el,'rows');
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el(inds1,:)=[edge2(1),edge1(1),1];
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[~,inds2] = ismember([edge2(2),edge2(1),1],el,'rows');
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el(inds2,:)=[edge2(2),edge1(2),1];
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end
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