Extend a matrix diagonally

I am trying to exted a 4 x 4 matrix to... lets say a 9 x 9 matrix while keeping the diagonal numbers. BUT the 9 x 9 matrix can easily be changed to 11 x 11 and so and so on. I looking for a for loop that will be to scale this matrix depending on input numbers.

2 1 0 0

1 2 1 0

0 1 2 1

0 0 1 2

2 1 0 0 0 0 0 0 0

1 2 1 0 0 0 0 0 0

0 1 2 1 0 0 0 0 0

0 0 1 2 1 0 0 0 0

0 0 0 1 2 1 0 0 0

0 0 0 0 1 2 1 0 0

0 0 0 0 0 1 2 1 0

0 0 0 0 0 0 1 2 1

0 0 0 0 0 0 0 1 2

Answer 1

[Matt J]

No need for a loop:

n=9;

result=toeplitz([2 1 zeros(1,n-2)])

result = 9×9

2 1 0 0 0 0 0 0 0 1 2 1 0 0 0 0 0 0 0 1 2 1 0 0 0 0 0 0 0 1 2 1 0 0 0 0 0 0 0 1 2 1 0 0 0 0 0 0 0 1 2 1 0 0 0 0 0 0 0 1 2 1 0 0 0 0 0 0 0 1 2 1 0 0 0 0 0 0 0 1 2

n=11;

result=toeplitz([2 1 zeros(1,n-2)])

result = 11×11

2 1 0 0 0 0 0 0 0 0 0 1 2 1 0 0 0 0 0 0 0 0 0 1 2 1 0 0 0 0 0 0 0 0 0 1 2 1 0 0 0 0 0 0 0 0 0 1 2 1 0 0 0 0 0 0 0 0 0 1 2 1 0 0 0 0 0 0 0 0 0 1 2 1 0 0 0 0 0 0 0 0 0 1 2 1 0 0 0 0 0 0 0 0 0 1 2 1 0 0 0 0 0 0 0 0 0 1 2 1

Answer 2

[Matt J]

See Create A Sparse Tridiagonal Matrix.