[J.Y.Won]

Hello all,
I'm making a C++ code solving diffusion equation gauss-seidel method.
It's just 2D problem and domain has length of 1 in x, y direction.

Solving this problem, I found something strange.

As my cell numbers gets larger(16x16, 32x32, 64x64 ... 1024x1024), the error between exact solution and my code goes down and up again.
I mean, error gets smaller until 128x128 and after that, error gets bigger...

So, until now I tried to find something wrong in my code.
And when I just translate my C++ code into matlab code, Error gets smaller without increasing again.....

I can't understand why this happen... can someone help me?
I attached my C++ code and matlab script.

Thanks,

[J.Y.Won]

problem solved...
It was because of the tolerance..