electricpy.math.rfft() raises NameError: name 'filter' is not defined

[marcostfermin]

Describe the bug

electricpy.math.rfft() calls filter.dnsample(...), but the module does not import or define filter, so the function raises a NameError whenever resample is truthy or numeric.

This is visible directly in the module code where filter.dnsample is referenced without any filter import/definition.

https://electricpy.readthedocs.io/en/latest/_modules/electricpy/math.html

Reproduction Code

# Setup
import numpy as np
import electricpy as ep

# Code which causes failure
x = np.sin(2*np.pi*5*np.linspace(0, 1, 1000, endpoint=False))
ep.math.rfft(x, dt=0.001, resample=True)  # triggers filter.dnsample(...)

Expected behavior

Return the FFT array (optionally downsampled) without raising a NameError.

Screenshots
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Desktop (please complete the following information):

• OS: [e.g. Linux]
• Python Version: 3.11.6
• Version: 0.4.0

Additional context

The error occurs because filter is never imported/defined in electricpy.math even though it’s used inside rfft.