iraf.net

NUMBER:	348
MODULE:	artdata.mkobjects
SYSTEM:	V2.10-V2.10.4p2
DATE:	Tue Oct  1 10:35:05 MST 1996
FROM:	valdes

BUG:	The routine for computing Poisson deviates does not check for
	negative input values which can lead to a floating point
	exception.  This routine can be called with negative values if the
	objects being created have negative values and the 'poisson'
	parameter is yes.  Negative values in the model objects can occur
	if image template models are used either for the objects or for the
	PSF.  The workarounds are to make sure the object models do not
	have negative values, to use a 'background' parameter sufficiently
	large to make the object+background be non-negative, or to not add
	Poisson noise.  The first option is the rigorously correct
	solution.  The case that identified this bug was with an
	empirically generated PSF that produced some negative values at the
	edge of the PSF template.

STATUS:	The Poisson deviate routine now returns zero if the input
	Poisson mean is negative.