comparison Problems/private/spdiag.m @ 10:207a6ae9a76f version1.0

(none)

+function Y = spdiag(V,K)
+%SPDIAG Sparse diagonal matrices.
+%   SPDIAG(V,K) when V is a vector with N components is a sparse square
+%   matrix of order N+ABS(K) with the elements of V on the K-th diagonal. 
+%   K = 0 is the main diagonal, K > 0 is above the main diagonal and K < 0
+%   is below the main diagonal. 
+%
+%   SPDIAG(V) is the same as SPDIAG(V,0) and puts V on the main diagonal.
+%
+%   See also DIAG, SPDIAGS.
+
+
+%  Ron Rubinstein
+%  Computer Science Department
+%  Technion, Haifa 32000 Israel
+%  ronrubin@cs
+%
+%  June 2008
+
+
+if (nargin<2)
+  K = 0;
+end
+
+n = length(V) + abs(K);
+
+if (K>0)
+  i = 1:length(V);
+  j = K+1:n;
+elseif (K<0)
+  i = -K+1:n;
+  j = 1:length(V);
+else
+  i = 1:n;
+  j = 1:n;
+end
+
+Y = sparse(i,j,V(:),n,n);