In matrix of 100 x 100 in python, filling the off diagonal elements

Question

I'm trying to fill the off diagonal elements on a 100x100 matrix, as shown below in the matlab code, so how to duplicate it in python.

T=(2*t0*diag(ones(1,100)))-(t0*diag(ones(1,99),1))-(t0*diag(ones(1,99),-1))

So I know that the first terms of RHS will fill the diagonal of the matrix with the value 2*t0,

which I do in python as follows:

x = np.zeros((100,100))
np.fill_diagonal(x,2*t0)

but I don't know how to do the 2nd and the 3rd terms, I know that they will fill the values above and below the diagonal elements with value of -t0, not all the off diagonal values but only filling the upper and lower value of diagonal with -t0, rest all are zeros, but I don't know how to write the python code for it.

I found this code:

# diagonal with offset from the main diagonal
diag([1,2,3], k=1) 

will give output as:

array([[0, 1, 0, 0],
[0, 0, 2, 0],
[0, 0, 0, 3],
[0, 0, 0, 0]])

but how to apply it for a large matrix as in the case of my problem? I work in interactive python i.e. Anaconda, so which are the other packages that I can use for my problem?

Answer 1

From what you supply here np.diag, it is easy to do:

a = np.ones((1, 100))[0]
b = np.ones((1, 99))[0]
m = np.diag(a, 0) + np.diag(b, -1) + np.diag(b, 1)

m here is the 100x100 tridiagonal matrix

Update:

I found a link here on a similar problem, have a look as well.