spyrit.core.torch.walsh_matrix_2d

spyrit.core.torch.walsh_matrix_2d(n)

2D Walsh-ordered Hadamard matrix.

This is the matrix \(A\in\mathbb{R}^{n^2 \times n^2}\) such that \(Ax\) represents the 2D Hadamard transform of the vectorised image \(x\).

Args:

n (int): Order of the transform \(n\), which must be a power of two.

Raises:

ValueError: If n is not a positive integer that is a power of 2.

Returns:

torch.Tensor: Matrix \(A\) with shape \((n^2,n^2)\).