Creates a sparse block diagonal matrix from a 3D array. Given an [mxnxk] matrix A, construct a sparse block diagonal matrix B of dims [m*k x n*k], containing k blocks of size mxn each, where each block i is taken from A(:,:,i). When computing B, a time consuming step is to compute a series of indices. These indices are fixed for given dims of A and can be re-used. spBlkDiag's additional input/output can be used to cache these indices. USAGE [B, inds] = spBlkDiag( A, [inds] ) INPUTS A - [m x n x k] input matrix of k mxn blocks inds - cached indices for faster computation OUTPUT B - [m*k x n*k] sparse block diagonal matrix with k mxn blocks inds - cached indices for faster computation EXAMPLE A=rand(3,4,2); B=spBlkDiag(A); full(B) See also SPARSE, BLKDIAG Piotr's Image&Video Toolbox Version 2.35 Copyright 2009 Piotr Dollar. [pdollar-at-caltech.edu] Please email me if you find bugs, or have suggestions or questions! Licensed under the Lesser GPL [see external/lgpl.txt]