function y = mpyL( L, lambda, x ) % mpyL multiply vector by L factor from LTL or LTDL % mpyL(L,lambda,x) computes L*x where L is the lower-triangular matrix from % either LTL or LTDL and lambda is the parent array describing the sparsity % pattern in L. n = size(L,1); y = x; % to give y same dimensions as x for i = 1:n y(i) = L(i,i) * x(i); j = lambda(i); while j ~= 0 y(i) = y(i) + L(i,j) * x(j); j = lambda(j); end end