function y = ForwardSub(A,b)
% The function solves a system of linear equations ax = b
%Step 4 (page 122).
% where a is lower triangular matrix by using forward 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(1,1)=b(1)/A(1,1);
for i=2:n
    y(i,1)=(b(i)-A(i,1:i-1)*y(1:i-1,1)) ./A(i,i);
end