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ISIS image subtraction program; trouble running

  1. Jun 29, 2010 #1
    Hi, I'm a bit new to the forums, this is my first post in fact, but I didn't know where else to go for help on this kind of matter.

    I'm not sure if anyone here has used ISIS image subtraction program written by Alard, available online at http://www2.iap.fr/users/alard/package.html, but I'm hoping someone has.

    I'm currently working on a bit of research that requires PSF matching to work, and this program should easily take care of that. However, I can't find any documentation other than his tutorial on how to use it.

    That would be fine, as I have it installed, but it fails during the second step of the tutorial (the ref.csh) on my data.

    Specifically, I get "Run error....Singular matrix in routine LUDCMP
    Goodbye ! "

    I think it has something to do with the stamping process, since it says the sigma and median of my image are both zero before this, and that the number of stamps is 0.

    Here's hoping someone is able to help, it's driving me a bit insane. Thanks in advance!
  2. jcsd
  3. Sep 26, 2011 #2
    I am having the same problem!
    Did you figure it out??
    please help!
  4. Apr 12, 2012 #3
    I had this problem. The problem originates when finding the astrometric solution (i.e. when using ./interp.csh). Check your interp_ files and see if the pixel value is 1 at every (or most) pixels. If so, this is what causes the problem.

    Try adding 10,000 ADU to each pixel in the file. You can do this in IRAF or with PyFits.

    IRAF: imarith file.fits + 10000 output.fits
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