function y = mpyLi( L, lambda, x ) % mpyLi multiply vector by inverse of L factor from LTL or LTDL % mpyLi(L,lambda,x) computes inv(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); for i = 1:n j = lambda(i); while j ~= 0 x(i) = x(i) - L(i,j) * x(j); j = lambda(j); end x(i) = x(i) / L(i,i); end y = x;