Hi Pete,

Apparently this was present in PDL with the first commit of the lookup tables 
<https://github.com/PDLPorters/pdl/commit/632a7d02dbad7947a02cb80292faa7e998447e77#diff-dbee01a9760c106bbd8be81f0e77f926f22a6b3d4df983e60e66039a07acdab6>
 in 2000.  My guess is it was either a copy-paste error or was present in the 
Starlink GAIA software from which the LUTs were taken.

PDL::Graphics::LUT as well as PDL::Graphics::PGPLOT is now in PGPLOT: 
https://github.com/PDLPorters/perl5-PGPLOT.  Today I created a pull request 
that fixes the ramps ramp.fits and neg.fits and also the table ramp.fits with 
more accurate values and without the wrinkle you mentioned.

best,
Derek

> On Jul 5, 2023, at 11:09 PM, Peter Ratzlaff via pdl-general 
> <[email protected]> wrote:
> 
> [EXTERNAL EMAIL]
> 
> I ran into this when experimenting with the giza PGPLOT substitution. giza's 
> implementation of pgctab() fails unless each successive ramp value is greater 
> than the previous. But,
> 
> $ perl -MPDL -MPDL::Graphics::LUT -le 'my ($r) = rfits 
> "$PDL::Graphics::LUT::rampdir/ramp.fits"; print $r->slice("150:154");'
> [0.58824 0.59608     0.6 0.59608 0.60392]
> 
> Is this a mistake of some sort, or is there a reason it is non-increasing?
> 
> Thanks,
> Pete
> 
> 
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