Data cube with one exposure (i.e. `cube.shape[0]==1`) causes indexing or division error.

[vandalt]

When using a data cube with only one exposure (i.e. cube.shape[0]==1), I encountered two errors in extract_bs():

• An IndexError if clipping had been done before and rejected the only frame in in the cube and extract_bs() had an empty input.

  Error message

    bs = amical.extract_bs(
    File "/home/vandal/projects/amical/amical/mf_pipeline/bispect.py", line 1138, in extract_bs
      ft_arr, n_ps, npix = _construct_ft_arr(cube)
    File "/home/vandal/projects/amical/amical/mf_pipeline/bispect.py", line 227, in _construct_ft_arr
      n_pix = cube.shape[1]
    IndexError: tuple index out of range
  

• A ZeroDivisionError if no clipping was done and extract_bs() received a cube with one frame.

  Error message

   bs = amical.extract_bs(
   File "/home/vandal/projects/amical/amical/mf_pipeline/bispect.py", line 1242, in extract_bs
       v2_quantities = _compute_v2_quantities(v2_arr_unbiased, bias_arr, n_blocks)
   File "/home/vandal/projects/amical/amical/mf_pipeline/bispect.py", line 537, in _compute_v2_quantities
       ind2 = (k + 1) * n_ps // (n_blocks - 1)
   ZeroDivisionError: integer division or modulo by zero
  

As discussed with @DrSoulain, this should not occur often and is currently not supported. It might still be worth adding an error to catch these two cases in extract_bs and raise a more informative error message to clarify what is happening.

[neutrinoceros]

can you share a self-contained reproducible example ?

[vandalt]

Yes! extract_bs() needs a file, so I'm using one of the example files in doc/NRM_DATA. This works on my machine from the amical/doc directory:

from pathlib import Path
from astropy.io import fits
from amical import extract_bs
from amical.data_processing import select_data

eg_file = Path("NRM_DATA/t_binary_s=147.7mas_mag=6.0_dm=6.0_posang=46.6__F430M_81_flat_x11__00.fits")

data = fits.getdata(eg_file)[:1]

# Uncomment this line to get the IndexError in extract_bs
# data = select_data(data, clip=True, display=False)

extract_bs(data, eg_file, "g7")

[vandalt]

Would this be a good solution ?

• select_data shows a warning if it clears a data cube of all its exposures (to let users know, even in cases where nothing is done with the cube after. An empty cube is probably not desirable, but not critical in the sense that users can just check for this and skip empty cubes
• extract_bs() check both cases (length 1 or empty) and raises and error. The two cases are critical for extraction, and result in error in private functions called by extract_bs()

[neutrinoceros]

Sorry for the delay. Yes, I believe that it would be a great way to handle things.