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