function y = BackwardSub(A,b)
% The function solves a system of linear equations ax = b
% where a is an upper triangular matrix by using back substitution.
% Input variables:
% a The matrix of coefficients.
% b A column vector of constants.
% Output variable:
% y A column vector with the solution.
n=length(b);
y(n,1)=b(n)/A(n,n);
for i=n-1:-1:1
    y(i,1)=(b(i)-A(i,i+1:n)*y(i+1:n,1)) ./A(i,i);
end