Pycraf atm module results in error when running example

[leonardoghizoni]

The path attenuation example returns an error for the gain computation:

File "pathattenuation.py", line 32, in
axes[0, 1].plot(_freqs, (-total_atten).to(cnv.dimless).value, linestyle, label=label)
File "/home/lghizoni/.local/lib/python3.6/site-packages/astropy/units/function/core.py", line 574, in array_ufunc
.format(function.name))
astropy.units.core.UnitTypeError: Cannot use ufunc 'negative' with function quantities

The problem seems to be the "(-total_atten)"

[bwinkel]

This appears to be a problem of the astropy.units package, which is used for physical units support (in particular logarithmic units). What astropy version do you have installed? On recent versions of astropy the problem disappeared (at least on my machine). A (nasty) work-around has always been to force the unit to the linear-scale first, e.g.,

(-total_atten).to(cnv.dimless).value

would be equivalent to

(1 / total_atten.to(cnv.dimless)).value