warnings emitted during divide by zero and invalid value encountered in multiply

[falkben]

we get a bunch of RuntimeWarnings on the last few steps of pipeline.

Possibly consider handling the divide/mult. differently (exclude zeros w/ np.where etc) to avoid these warnings, which might confuse the user.

Summing the images of filter uw1...
combine.py:224: RuntimeWarning: invalid value encountered in true_divide
  coicorr_rel = sum_datacube[2] / primary
combine.py:229: RuntimeWarning: invalid value encountered in true_divide
  notnan = np.isfinite(datacube[0]/datacube[1])
combine.py:230: RuntimeWarning: invalid value encountered in true_divide
  denom[notnan] += (datacube[0]/datacube[1])[notnan]
combine.py:231: RuntimeWarning: invalid value encountered in true_divide
  f_coi = primary / denom
combine.py:236: RuntimeWarning: invalid value encountered in true_divide
  notnan = np.isfinite(datacube[0]/datacube[3])
combine.py:237: RuntimeWarning: invalid value encountered in true_divide
  denom[notnan] += (datacube[0]/datacube[3])[notnan]
combine.py:238: RuntimeWarning: invalid value encountered in true_divide
  f_zp = primary / denom
combine.py:241: RuntimeWarning: invalid value encountered in sqrt
  poisson_rel = 1./np.sqrt(primary)
combine.py:241: RuntimeWarning: divide by zero encountered in true_divide
  poisson_rel = 1./np.sqrt(primary)
Normalizing the total sky image of filter uw1...
combine.py:274: RuntimeWarning: invalid value encountered in true_divide
  datacube[0] = datacube[0]/exp_data
Calibration and aperture correction (calibration.py)
Converting the units of the final image from counts/s to Jy and correcting for the aperture calibration...
calibration.py:48: RuntimeWarning: invalid value encountered in multiply
  poisson = hdulist[0].data[4] * primary