Why is my custom Conjugate gradient solver and MATLAB pcg() do not have the same result?

Based on some literature I tried to implement a C code based on a Matlab code for conjugate gradient solver. However, When I tried to compare the code published on Wikipedia with MATLAB pcg() function as follows:

rng default
A = sprand(100,100,.5);
A = A'*A;
b = sum(A,2);
x1 = pcg(A, b, 1e-4, 150);
x2 = conj_grad(A, b, 1e-4, 150);
function x_i = conj_grad(m_A, v_b, tol, iter)
x_i = v_b;
r = v_b - m_A * x_i;
p = r;
rsold = r' * r;
for i = 1:iter Ap = m_A * p; alpha = rsold / (p' * Ap); x_i = x_i + alpha * p; r = r - alpha * Ap; rsnew = r' * r; if sqrt(rsnew) < tol fprintf('cg converged at iteration %d to a solution with relative residual %f', i, sqrt(rsnew)); break; end p = r + (rsnew / rsold) * p; rsold = rsnew;
end
end

I discovered that the custom made function does not converge as pcg() and the results are somehow different, for example:

conj_grad() pcg()
----------------------
1.057764 1.050005
0.959692 0.957766
1.055046 1.017192
0.990600 1.012397
0.945796 0.966080
1.017147 0.989121
0.957176 0.975864
1.084515 1.087173
1.057552 1.047540
1.003535 1.005227
1.010863 0.995646 

Could someone give some hints, please? Thank you

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