randomize_graph_partial_und.m
257e25cb59ccmaster

randomize_graph_partial_und.m
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			function A = randomize_graph_partial_und(A,B,maxswap)
			% RANDOMIZE_GRAPH_PARTIAL_UND Swap edges with preserved degree sequence
			%
			% A = RANDOMIZE_GRAPH_PARTIAL_UND(A,B,MAXSWAP) takes adjacency matrices A
			% and B and attempts to randomize matrix A by performing MAXSWAP
			% rewirings. The rewirings will avoid any spots where matrix B is
			% nonzero.
			%
			% Inputs: A, undirected adjacency matrix
			% B, edges to avoid
			% MAXSWAP, number of rewirings
			%
			% Outputs: A, randomized matrix
			%
			% Richard Betzel, Indiana University, 2013
			%
			% Notes:
			% 1. Based on the script randmio_und.m.
			% 2. Graph may become disconnected as a result of rewiring. Always
			% important to check.
			% 3. A can be weighted, though the weighted degree sequence will not be
			% preserved.
			%

			[i,j] = find(triu(A,1));
			m = length(i);
			nswap = 0;
			while nswap < maxswap
			while 1
			e1 = randi(m); e2 = randi(m);
			while e2 == e1
			e2 = randi(m);
			end
			a = i(e1); b = j(e1);
			c = i(e2); d = j(e2);
			if all(a~=[c,d]) && all(b~=[c,d])
			break
			end
			end
			if rand > 0.5
			i(e2) = d; j(e2) = c;
			c = i(e2); d = j(e2);
			end
			if ~(A(a,d) \|\| A(c,b) \|\| B(a,d) \|\| B(c,b))
			A(a,d) = A(a,b); A(a,b) = 0;
			A(d,a) = A(b,a); A(b,a) = 0;
			A(c,b) = A(c,d); A(c,d) = 0;
			A(b,c) = A(d,c); A(d,c) = 0;
			j(e1) = d;
			j(e2) = b;
			nswap = nswap + 1;
			end
			end