How to solve a 2D PDE with backward Euler?

Hi, i have to solve the 2D heat equation:

∂T/∂t = α∇^2 T = α(∂^2T/∂x^2 + ∂^2T/∂y^2)

It is given that at the 4 boundaries the T is 0. I've already written some code, but it doesn't works. Can someone review my code and help me? The error occurs at the end, when the new T are put in a matrix. The code has been added as an attachment.

Answer 1

[M]

At line 58, you are trying to access the 11th element of the Number matrix, but its dimensions are 10 x 10, so you get an error.