ValueError: number of diagonals (1) does not match the number of offsets (3)

In python 2.7, I'm trying to create a sparse matrix with 3 diagonals. The matrix should look like this:

[[ 10   0   0   0 -19   0   0   0  10   0   0   0  ...  0]
 [  0  10   0   0   0 -19   0   0   0  10   0   0  ...  0]
 [  0   0  10   0   0   0 -19   0   0   0  10   0  ...  0]
 [ -1   1   1   0   0   0   0   0   0   0   0   0  ...  0]]

My code is

import numpy as np
import numpy.matlib
import scipy.sparse

Dk = np.array([[ 10.], [ 10.],[ 10.]])
Ns = 3
N = 100
z = np.array([[-1.],
   [ 1.],
   [ 1.]])

dg0 = np.array([numpy.matlib.repmat(1-2*Dk,1,1)])
dgn = np.array([numpy.matlib.repmat(Dk,1,1)])
dgp = np.array([numpy.matlib.repmat(Dk,1,1)])

B = np.zeros((Ns+1,N))

dg0 = np.append(dg0,0) 
dgn = np.append(dgn,0)
dgp = np.append(dgp,0)
zerosN1 = np.zeros((1,Ns+1))
zerosN2 = np.zeros((1,2*(Ns+1)))
dg0 = np.append(zerosN1,dg0)
dgp = np.append(zerosN2,dgp)

data0 = np.array([dgn,dg0,dgp])
diags0 = np.array([0,Ns+1,2*(Ns+1)])

B = scipy.sparse.spdiags(data0, diags0, Ns+1, N)
B = scipy.sparse.lil_matrix(B)
zerosN = np.zeros((1,N-Ns))
B[3] = np.append(z,zerosN)

I am getting an error: ValueError: number of diagonals (1) does not match the number of offsets (3)

I don't understand what's wrong. I'd appreciate any help.

Solution

Your problem is that data0 looks like this:

array([array([ 10.,  10.,  10.,   0.]),
       array([  0.,   0.,   0.,   0., -19., -19., -19.,   0.]),
       array([  0.,   0.,   0.,   0.,   0.,   0.,   0.,   0.,  10.,  10.,  10.,
         0.])], dtype=object)

I'm not sure what you're doing with repmat (or a lot of parts of your program, for that matter), as all you have to do to create a sparse matrix from diagonals is provide the same number of diagonals (of the same length) as the offsets provided. Thus, this should suffice:

flattened_Dk = Dk.ravel()
data0 = [flattened_Dk, 1-2*flattened_Dk, flattened_Dk]
B = scipy.sparse.diags(data0, diags0, shape=(Ns,N))