[FIXED] Create array/tensor of cycle shifted arrays

Issue

I want to create 2d tensor (or numpy array, doesn't really matter), where every row will be cycle shifted first row. I do it using for loop:

import torch
import numpy as np

a = np.random.rand(33, 11)
miss_size = 64
lp_order = a.shape[1] - 1
inv_a = -np.flip(a, axis=1)
mtx_size = miss_size+lp_order   # some constant
mtx_row = torch.cat((torch.from_numpy(inv_a), torch.zeros((a.shape[0], miss_size - 1 + a.shape[1]))), dim=1)
mtx_full = mtx_row.unsqueeze(1)
for i in range(mtx_size):
        mtx_row = torch.roll(mtx_row, 1, 1)
        mtx_full = torch.cat((mtx_full, mtx_row.unsqueeze(1)), dim=1)

unsqueezing is needed because I stack 2d tensors into 3d tensor

Is there more efficient way to do that? Maybe linear algebra trick or more pythonic approach.

Solution

You can use scipy.linalg.circulant():

scipy.linalg.circulant([1, 2, 3])
# array([[1, 3, 2],
#        [2, 1, 3],
#        [3, 2, 1]])

Answered By - Nils Werner