42 lines
1.3 KiB
Matlab
42 lines
1.3 KiB
Matlab
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% Finds the dual of a graph; a dual is the inverted nodes-edges graph
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% This is also called the line graph, adjoint graph or the edges adjacency
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%
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% INPUTs: adjacency (neighbor) list representation of the graph (see adj2adjL.m)
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% OUTPUTs: adj (neighbor) list of the corresponding dual graph and
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% cell array of [original] edges, i.e. the new nodes
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%
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% Note: This routine only works for undirected, simple graphs.
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% GB: last updated, Sep 23 2012
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function [dL,edge_array] = graphDual(L)
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dL={}; % initialize
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for i=1:length(L)
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for j=1:length(L{i})
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if i<=L{i}(j); dL{length(dL)+1}=[]; end
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end
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end
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edge_array={};
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for i=1:length(L)
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for j=1:length(L{i}) % add i,L{i}j to list of nodes
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if i<=L{i}(j); edge_array{length(edge_array)+1}= strcat(num2str(i),'-',num2str(L{i}(j))); end
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end
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for j=1:length(L{i}) % add i - L{i}j to list of edges
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for k=j+1:length(L{i})
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edge1=strcat(num2str(min([i,L{i}(j)])),'-',num2str(max([i,L{i}(j)])));
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edge2=strcat(num2str(min([i,L{i}(k)])),'-',num2str(max([i,L{i}(k)])));
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ind_edge1=find(ismember(edge_array, edge1)==1);
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ind_edge2=find(ismember(edge_array, edge2)==1);
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dL{ind_edge1}=unique([dL{ind_edge1},ind_edge2]);
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dL{ind_edge2}=unique([dL{ind_edge2},ind_edge1]);
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end
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end
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end
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