Error in instantaneous rate when passing a 1-dimensional kernel sigma [Bug]

[Kleinjohann]

Describe the bug
When passing a more than 0-dimensional sigma in the generation of a kernel and using said kernel to calculate the instantaneous firing rate an error is raised somewhere in fftconvolve.

To Reproduce

import neo
import elephant
import quantities as pq

st = neo.SpikeTrain([1]*pq.s, t_stop=2*pq.s)
kernel = elephant.kernels.GaussianKernel(sigma=[20]*pq.ms)

rate = elephant.statistics.instantaneous_rate(st,
                                              sampling_period=1*pq.ms,
                                              kernel=kernel)

returns

Traceback (most recent call last):
  File "reproduce_sigma_error.py", line 9, in <module>
    rate = elephant.statistics.instantaneous_rate(st,
  File "/home/kleinjohann/software/elephant/elephant/utils.py", line 79, in wrapper
    return func(*args, **kwargs)
  File "/home/kleinjohann/software/elephant/elephant/statistics.py", line 868, in instantaneous_rate
    rate = scipy.signal.fftconvolve(time_vectors,
  File "/home/kleinjohann/software/miniconda3/envs/elephant/lib/python3.8/site-packages/scipy/signal/signaltools.py", line 525, in fftconvolve
    raise ValueError("in1 and in2 should have the same dimensionality")
ValueError: in1 and in2 should have the same dimensionality

I tracked this down to

elephant/elephant/statistics.py

Line 852 in d0d3920

t_arr = np.linspace(-cutoff_sigma + median, stop=cutoff_sigma + median,

where t_arr gains an extra dimension since cutoff_sigma keeps the extra dimension of sigma.

Expected behavior
Either a more helpful error should be raised which tells me to fix the dimensionality of sigma, or different dimensionalities should be accounted for internally and no error should be raised.

Environment

• OS: Linux
• How I installed elephant: from source
• Python version: 3.8.1
• neo python package version: 0.9.0
• elephant version: d0d3920
• scipy version: 1.5.4

[Moritz-Alexander-Kern]

Thanks for reporting this.
I get the same error.

We will look into this, currently elephant.statistics.instantaneous_rate is undergoing changes with PR #453 in relation to #374.