python numpy roll with padding

Question

I\'d like to roll a 2D numpy in python, except that I\'d like pad the ends with zeros rather than roll the data as if its periodic.

Specifically, the following code<

Answer 1

You could also use numpy's triu and scipy.linalg's circulant. Make a circulant version of your matrix. Then, select the upper triangular part starting at the first diagonal, (the default option in triu). The row index will correspond to the number of padded zeros you want.

If you don't have scipy you can generate a nXn circulant matrix by making an (n-1) X (n-1) identity matrix and stacking a row [0 0 ... 1] on top of it and the column [1 0 ... 0] to the right of it.