[daip] random number generator in IMMOD (and likely others)

[Michael Bietenholz]

   I think there is something fishy with the random number generator in
IMMOD: two subsequent runs of IMMOD almost always seem to generate two
very highly correlated images.  Sometimes there is no shift, sometimes
there is a small horizontal shift.

Oddly enough, then I looked at the actual pixel values, they are not
identical.

Attached an IMVIM plot of two separate 256x256 images output by
IMMOD.  Very odd: the pixel values are highly correlated from
one run to the next, but not identical!

(31DEC07, midnight job today; but has been around for some time)

               michael b


-----relevant IMMOD inputs----------
AIPS 1: OPCODE     ' '                     Model types are:
AIPS 1:                                    'GAUS', 'DISK', 'RECT',
AIPS 1:                                    'SPHE', 'EXPD', 'POIN'
AIPS 1: NGAUS         1                    Number components to add
AIPS 1: FMAX       *all 0                  Peak of component (Jy)
AIPS 1:                                      0-> Use maximum value
AIPS 1: FPOS       *all 0                  (X,Y) position (pixels)
AIPS 1:                                      0-> Use position of max
AIPS 1: FWIDTH     *all 0                  (BMAJ, BMIN, PA) of comp.
AIPS 1:                                      (pixels,pixels,deg)
AIPS 1:                                      0->Use clean beam
AIPS 1: FLUX          1                    Noise level
AIPS 1: FACTOR        0                    Multiplication factor.
-------------- next part --------------
A non-text attachment was scrubbed...
Name: imvim.gif
Type: image/gif
Size: 10902 bytes
Desc: 
URL: <http://listmgr.nrao.edu/pipermail/daip/attachments/20071105/a1ae6fa8/attachment.gif>