speye - sparse identity matrix
Isp=speye(nrows,ncols) returns a sparse identity matrix Isp with nrows rows, ncols columns. (Non square identity matrix have a maximal number of ones along the main diagonal).
Isp=speye(A) returns a sparse identity matrix with same dimensions as A. If [m,n]=size(A), speye(m,n) and speye(A) are equivalent. In particular speye(3) is not equivalent to speye(3,3).