Create double row diagonal matrix in numpy

Question

I am trying to make a special diagonal matrix that looks like this:

[[1,1,0,0,0,0],
 [0,0,1,1,0,0],
 [0,0,0,0,1,1]]

It is slightly different from the question here: Make special diagonal matrix in Numpy

I tried tweaking the solution but couldn't quite get it. Appreciate any advice on how to achieve this efficiently.

`a = np.zeros((3, 6), dtype=int); j = np.arange(a.shape[1]); a[j // 2, j] = 1` — Warren Weckesser, Jan 31 '19 at 08:10
great!! please add it as an answer and i will accept it. thank you! — yl_low, Jan 31 '19 at 08:14

score 0 · Answer 1 · answered Jan 31 '19 at 08:19

Not as elegant as in comments, but :

a=4 # number of rows
b=a*2 #number of columns
np.array((([1]*2+[0]*b)*a)[:-b]).reshape(a,b)
array([[1, 1, 0, 0, 0, 0, 0, 0],
       [0, 0, 1, 1, 0, 0, 0, 0],
       [0, 0, 0, 0, 1, 1, 0, 0],
       [0, 0, 0, 0, 0, 0, 1, 1]])

works for any a.

Create double row diagonal matrix in numpy

1 Answers1