% Program Numerical Analysis
% Jan 10th      HW4
clc

clear
A=[5 -2 3;-3 9 1;2 -1 -7]

b=[-1;2;3];
x0=[0;0;0];
x=x0;
Iterations=1e6;
ApproximateValue=1e-10;
tic

    gamma=b-A*x;
    Q=gamma;
    rs=gamma'*gamma;
    disp('Calculating...')
    for i=1:Iterations
        Ap=A*Q;
        alpha=rs/(Q'*Ap);
        x=x+alpha*Q;
        gamma=gamma-alpha*Ap;
        rsnew=gamma'*gamma;
        if sqrt(rsnew)<ApproximateValue
              break;
        end
        Q=gamma+rsnew/rs*Q;
        rs=rsnew;
    end
    disp('Solution is:')
    x
    elapsedtime=toc