votes up 1

Denominator a must be 1-D.

Package:
scipy
github stars 8546
Exception Class:
ValueError

Raise code

    # cases where a ValueError is more appropriate, and it allows
    # b to be 2D.
    b = np.atleast_1d(b)
    if b.ndim != 1:
        raise ValueError("Numerator b must be 1-D.")
    a = np.atleast_1d(a)
    if a.ndim != 1:
        raise ValueError("Denominator a must be 1-D.")

    while len(a) > 1 and a[0] == 0.0:
        a = a[1:]
    if a.size < 1:
        raise ValueError("There must be at least one nonzero `a` coefficient.")

    if a[0] != 1.0:
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Ways to fix

votes up 2 votes down

If a is set to 2D array this error is raised.

How to to recreate the error:

pipenv install scipy numpy

from numpy import array, ones
from scipy.signal import lfilter, lfilter_zi, butter
b, a = butter(5, 0.25)
a = [a]
zi = lfilter_zi(b, a)
y, zo = lfilter(b, a, ones(10), zi=zi)
print(y)

---------------------------------------------------------------------------
ValueError                                Traceback (most recent call last)
<ipython-input-33-dbc16574d684> in <module>()
      2 from scipy.signal import lfilter, lfilter_zi, butter
      3 b, a = butter(5, 0.25)
----> 4 zi = lfilter_zi(b, [a])
      5 y, zo = lfilter(b, a, ones(10), zi=zi)
      6 print(y)

/usr/local/lib/python3.7/dist-packages/scipy/signal/signaltools.py in lfilter_zi(b, a)
   3589     a = np.atleast_1d(a)
   3590     if a.ndim != 1:
-> 3591         raise ValueError("Denominator a must be 1-D.")
   3592 
   3593     while len(a) > 1 and a[0] == 0.0:

ValueError: Denominator a must be 1-D.

Fixed:

from numpy import array, ones
from scipy.signal import lfilter, lfilter_zi, butter
b, a = butter(5, 0.25)
# a = [a]
zi = lfilter_zi(b, a)
y, zo = lfilter(b, a, ones(10), zi=zi)
print(y)

[1. 1. 1. 1. 1. 1. 1. 1. 1. 1.]

Aug 26, 2021 kellemnegasi answer
kellemnegasi 31.6k

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