I translated a Matlab function to create an Overcomplete Discrete Cosine Transform matrix to represent 1D signals in such a vector space into Python.

Matlab function

function D = odctdict(n,L)
%ODCTDICT Overcomplete DCT dictionary.
%  D = ODCTDICT(N,L) returns the overcomplete DCT dictionary of size NxL
%  for signals of length N.
%
%  See also ODCT2DICT, ODCT3DICT, ODCTNDICT.    

D = zeros(n,L);
D(:,1) = 1/sqrt(n);
for k = 2:L
  v = cos((0:n-1)*pi*(k-1)/L)';
  v = v-mean(v);
  D(:,k) = v/norm(v);
end

      

        
        
        
      

    

Python translation function

import numpy as np


def odct1dict(n, l):
    """
    1-D Overcomplete DCT dictionary.

    D = odct1dict(N, L) returns the overcomplete DCT dictionary of size NxL
    for signals of length N.

    :param n: signal size
    :type n: int
    :param l: number of atoms
    :type l: int
    :return: 1-D Overcomplete DCT dictionary NumPy array
    """

    d = np.zeros((n, l))
    d[:, 0] = 1 / np.sqrt(n)

    for k in range(1, l):
        v = np.transpose(np.cos(np.arange(0, n) * np.pi * k * l))
        v = v - np.mean(v)
        d[:, k] = v / np.linalg.norm(v)

    return d

      

        
        
        
      

    

I use both PyCharm IDE Python, and this software is a warning that I do not understand the instructions v = np.transpose(np.cos(np.arange(0, n) * np.pi * k * l))

inside the loop for, in particular, for the argument of the function np.transpose

, np.cos(np.arange(0, n) * np.pi * k * l)

.

The expected type is "Union [ndarray, Iterable]", instead "int" is less ...

This check detects type errors in function call expressions. In connection with dynamic dispatch and duck printing, this is possible in a limited but useful number of cases. You can specify the types of function parameters in docstrings or in Python 3 function annotations.

Can you explain this warning for me? And how do you fix it? What is the correct way to write such an instruction?