Parallel PS script fails for too large nrun (or too few structures)

[max-veit]

This error usually happens when I ask sagpr_parallel_get_PS to try to split a trajectory into too many parallel calculations, thereby ending up with an empty slice which throws a spanner in the works. But I have an automated workflow that sometimes spits out very short trajectories, so it would be nice if the parallel PS script could handle these cases gracefully (basically, if -nrun < len(traj), only run the first len(traj) calculations in parallel and don't try to run more).

For reference, a typical error backtrace is below:

...skipping...
IOError: [Errno 2] No such file or directory: 'cubic_tetra_transition/PS0v_seg015.npy'
Traceback (most recent call last):
  File "/home/veit/SOAPFAST//bin/sagpr_get_PS", line 276, in <module>
    main()
  File "/home/veit/SOAPFAST//bin/sagpr_get_PS", line 270, in main
    get_power_spectrum(lam,frames,nmax=nmax,lmax=lmax,rc=rcut,sg=sig,ncut=ncut,periodic=periodic,outfile=outfile,cw=cweight,subset=subset,initial=initial,sparsefile=sparsefile,sparse_options=sparse_options,cen=cen,spec=spec,atomic=atomic,all_radial=all_radial,useall=useall,xyz_slice=xyz_slice,get_imag=get_imag)
    natmax    = len(max(all_names, key=len))
ValueError: max() arg is an empty sequence
Traceback (most recent call last):
  File "/home/veit/SOAPFAST//bin/sagpr_get_PS", line 276, in <module>
    main()
  File "/home/veit/SOAPFAST//bin/sagpr_get_PS", line 270, in main
    get_power_spectrum(lam,frames,nmax=nmax,lmax=lmax,rc=rcut,sg=sig,ncut=ncut,periodic=periodic,outfile=outfile,cw=cweight,subset=subset,initial=initial,sparsefile=sparsefile,sparse_options=sparse_options,cen=cen,spec=spec,atomic=atomic,all_radial=all_radial,useall=useall,xyz_slice=xyz_slice,get_imag=get_imag)
    natmax    = len(max(all_names, key=len))
ValueError: max() arg is an empty sequence
Traceback (most recent call last):
  File "/home/veit/SOAPFAST//bin/sagpr_get_PS", line 276, in <module>
    main()
  File "/home/veit/SOAPFAST//bin/sagpr_get_PS", line 270, in main
    get_power_spectrum(lam,frames,nmax=nmax,lmax=lmax,rc=rcut,sg=sig,ncut=ncut,periodic=periodic,outfile=outfile,cw=cweight,subset=subset,initial=initial,sparsefile=sparsefile,sparse_options=sparse_options,cen=cen,spec=spec,atomic=atomic,all_radial=all_radial,useall=useall,xyz_slice=xyz_slice,get_imag=get_imag)
    natmax    = len(max(all_names, key=len))
ValueError: max() arg is an empty sequence

(this happens when using -nrun 4 on a trajectory of length 1)

[harpaf13]

I recently ran into this same issue and I can confirm that switching to this branch solved the issue and instead printed out no frames passed to get_power_spectrum however, as written the sagpr_get_parallell_PS script still fails when using the -a flag because it searches explicitly for PS_output_??.npy

With a few modifications to the stack_power_spectra.py script I can get the -a flag working successfully with the sagpr_get_parallell_PS script if you are interested in looking at a PR for that just let me know.