how can i create a 400 by 400 matrix with a pattern?

The matrix is 400 by 400 and i need a -1 2 -1 pattern starting with 2. Like this:

Answer 1

[Guillaume]

full(gallery('tridiag', 400))

If the subdiagonal, diagonal and superdiagonal were anything other than -1, 2, 1, for example: 1, 2, 3 respectively:

fulll(gallery('tridiag', 400, 1, 2, 3))

Another way:

toeplitz([2, -1, repelem(0, 398)])