Function first_row_to_first_col

pub const fn first_row_to_first_col<const N: usize, T: Copy>(
    v: &[T; N],
) -> [T; N]

Given the first row of a circulant matrix, return the first column.

For example if, v = [0, 1, 2, 3, 4, 5] then output = [0, 5, 4, 3, 2, 1], i.e. the first element is the same and the other elements are reversed.

This is useful to prepare a circulant matrix for input to an FFT algorithm, which expects the first column of the matrix rather than the first row (as we normally store them).

NB: The algorithm is inefficient but simple enough that this function can be declared const, and that is the intended context for use.