57 lines
1.2 KiB
Matlab
57 lines
1.2 KiB
Matlab
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% Create a k-regular graph.
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% Note: No solution if k and n are both odd.
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%
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% INPUTs: n - # nodes, k - degree of each vertex
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% OUTPUTs: el - edge list of the k-regular undirected graph
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%
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% Other routines used: symmetrizeEdgeL.m
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% GB: last updated, Oct 28 2012
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function el = kregular(n,k)
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el=[];
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if k>n-1; fprintf('a simple graph with n nodes and k>n-1 does not exist\n'); return; end
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if mod(k,2)==1 && mod(n,2)==1; fprintf('no solution for *n* and *k* both odd\n'); return; end
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half_degree=floor(k/2); % k/2 if k even, else (k-1)/2
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for node=1:n
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for kk=1:half_degree
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node_f=mod(node+kk,n);
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if node_f==0; node_f=n; end
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if not(ismember([node,node_f,1],el,'rows'))
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el = [el; node node_f 1];
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end
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node_b=mod(node-kk,n);
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if node_b==0; node_b=n; end
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if not(ismember([node,node_b,1],el,'rows'))
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el = [el; node node_b 1];
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end
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end
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end
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if mod(k,2)==1 && mod(n,2)==0
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% connect mirror nodes
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for node=1:n/2
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node_m=mod(node+n/2,n);
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if node_m==0; node_m=n; end
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if not(ismember([node,node_m,1],el,'rows'))
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el = [el; node node_m 1];
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end
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end
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end
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el=symmetrizeEdgeL(el);
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