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Dear IRAF gurus,

I have a script which repeatedly calls pvector and is supposed to put several pvector plots in one output FITS file. It works fine on one of my computers (a laptop), but fails on several other computers. Each computer is running Linux Mint 18.0 (or 18.3) and each has IRAF version 2.16.1.

I want my students to be able to use the script without me so it's been driving me nuts.

Here are the first 3 lines of the script (only two lines are needed to reproduce failure):
pvector N7727Rbsr.fits xc=1090.91 yc=1067.62 width=1 theta=235 length=140 vec_out=RbsrPVs2 out_typ=image
pvector N7727Rbsr.fits xc=1088.91 yc=1067.62 width=1 theta=235 length=140 vec_out=RbsrPVs2 out_typ=image
pvector N7727Rbsr.fits xc=1089.91 yc=1067.62 width=1 theta=235 length=140 vec_out=RbsrPVs2 out_typ=image

Here is the behavior when it fails:

ecl> cl < pveesimgR.cl
ERROR: Error opening output image.
called as: `cl ()'
It does create a FITS file, but it only contains one, 1-D image instead of multiple FITS extensions.

And when it succeeds (on the laptop), it has no error message and produces exactly the kind of multi-extension FITS file I'm expecting. I have tried the script with "append=yes" on each line and it doesn't help. I also use epar to set append=yes in the pvector pars.

I suspect the issue lies with cfitsio or some other libraries but I don't know. Any ideas?

thanks for any help,
Jason