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- function A = spm_vb_incidence(edges,N)
- % Edge-node incidence matrix of a graph
- % FORMAT A = spm_vb_incidence(edges,N)
- %
- % edges [Ne x 2] list of neighboring voxel indices
- % N number of nodes (cardinality of node set)
- %
- % Ne number of edges (cardinality of edge set)
- % A [Ne x N] matrix - is the discrete analogue of the grad operator
- % A(ij,k) +1 if i=k, -1 if j=k, 0 otherwise, where ij is the edge
- % connecting nodes i and j, and k is in node set
- %__________________________________________________________________________
- % Copyright (C) 2005-2014 Wellcome Trust Centre for Neuroimaging
- % Lee Harrison
- % $Id: spm_vb_incidence.m 6079 2014-06-30 18:25:37Z spm $
- % Number of edges
- Ne = size(edges,1);
- % Number of nodes (if N is not specified)
- if nargin < 2
- N = max(edges(:));
- end
- % Edge-node incidence matrix
- A = sparse([1:Ne,1:Ne],[edges(:,1),edges(:,2)],...
- [ones(Ne,1),-ones(Ne,1)],Ne,N);
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