function [x] = lutri(A,P,b);
%
% use the LU factorization stored in A and P to solve a 
% triangular system LUx=Pb.
%
% calling sequence: [x] = lutri(A,P,b);
%
% input:
%   A = square data structure containing L and U factors
%   P = vector containing coded form of permutation P
%   b = right-hand side
% 
% output:
%   x = solution of LUx=Pb
%