gpu_notes

Comments on Slack from James Perry about GPU testing work he did.
https://lsstc.slack.com/archives/CHXKSF3HC/p1696253564727889

Chris suggested that I make sure to pass on any documentation/tools I have developed and used
during my GalSim work. Most of what I have done is documented in the normal places on GitHub,
or discussed on this channel. But there are a couple of small things that may not be:

https://github.com/jamesp-epcc/GalSimGPUTest
- This is a test case and build scripts for running the GPU sensor model in pure C++,
no Python layer.  I developed this so that I could get on with adding GPU acceleration to the
code without having to worry about the complexities of setuptools etc. until later on.
I'm not sure how much use it will be to anyone going forward, but just in case, here it is.

https://jamesp-epcc.github.io/lsst/galsim-gpu.html
- This is my notes on how to build and run GalSim on Perlmutter with GPU acceleration enabled.