  function x = backsolv0(A,b) 
% function x = backsolv0(A,b) 
% Solves an upper triangular system
% by back-substitution. 
%----------------------------------
 n = size(A,1); 
 x = zeros(n,1);  
 for i=n:-1:1
     t = b(i);
     for j=i+1:n
         t = t - A(i,j)*x(j) ;
     end
     x(i) = t/A(i,i) ;
 end 
 

