How to construct the n*n matrices, like below:

I know I can use diag to build that matrices, but I did not figured out how to build like that.

Answer 1

[Walter Roberson]

diag(vector_of_2s) - diag(vector_of_ones, 1) - diag(vector_of_ones, -1)

[Shangwen Chen]

Thanks for your helping!

Answer 2

[Stephen23]

Use toeplitz:

>> n = 10;
>> toeplitz([2,-1,zeros(1,n-2)])
ans =
   2  -1   0   0   0   0   0   0   0   0
  -1   2  -1   0   0   0   0   0   0   0
   0  -1   2  -1   0   0   0   0   0   0
   0   0  -1   2  -1   0   0   0   0   0
   0   0   0  -1   2  -1   0   0   0   0
   0   0   0   0  -1   2  -1   0   0   0
   0   0   0   0   0  -1   2  -1   0   0
   0   0   0   0   0   0  -1   2  -1   0
   0   0   0   0   0   0   0  -1   2  -1
   0   0   0   0   0   0   0   0  -1   2

[Shangwen Chen]

Thanks for your helping!

Answer 3

[Bruno Luong]

Such matrix is a FEM/discrete laplacian, and I strongly recommend using sparse matrix whene ever solving PDE.

n = ...
S = spdiags(ones(n,1)*[-1 2 1],[-1 0 1],n,n);

[Shangwen Chen]

Thanks for your helping!