How to double the dimension of a matrix while quartering the values?

Question

I want to achieve this:

a = np.array ([[1, 2],
               [2, 1]])

b = np.array ([[0.25, 0.25, 0.5, 0.5],
               [0.25, 0.25, 0.5, 0.5],
               [0.5, 0.5, 0.25, 0.25],
               [0.5, 0.5, 0.25, 0.25])

Mathematically they r not the same matrices. But i think you get the idea what i want to do. I want to double the dimension of a matrix. But therefore i want to keep the information from the initial matrix a by take the quarter for the four corresponding cells.

Does some1 knows how to do this efficiently in numpy?

Answer 1

You can use two repeat functions over both axis and then a simple division:

In [8]: np.repeat(np.repeat(a, 2, 1), 2, 0)/4
Out[8]: 
array([[0.25, 0.25, 0.5 , 0.5 ],
       [0.25, 0.25, 0.5 , 0.5 ],
       [0.5 , 0.5 , 0.25, 0.25],
       [0.5 , 0.5 , 0.25, 0.25]])