Multiplication with fundamental nullspace basis
W = fzmult(A,V)
W = fzmult(A,V,'transpose')
[W,L,U,pcol,P] = fzmult(A,V)
W = fzmult(A,V,transpose,L,U,pcol,P)
W = fzmult(A,V) computes the product W of matrix Z with matrix V, that is, W = Z*V, where Z is a fundamental basis for the nullspace of matrix A. A must be a sparse m-by-n matrix where m < n, rank(A) = m, and rank(A(1:m,1:m)) = m. V must be p-by-q, where p = n-m. If V is sparse W is sparse, else W is full.
The nullspace basis matrix Z is not formed explicitly. An implicit representation is used based on the sparse LU factorization of A(1:m,1:m).