Particle Histogram 2D

[ax3l]

Need for a reduced diagnostics addition: general 2D particle histogram (think: "np.histogram2d").

• Applications: phase space, energy-emittance plots, etc.
  • Would be useful for WarpX, ImpactX, and HiPACE++
• Size: fit into local GPU memory, e.g., default 1024^2
• 3 parser functions: axis1, axis2, filter
  • All three into the kernel
  • No RNG needed
• Can be loosely on the exiting reduced diagnostics ParticleHistogram
• Extension: expose arbitrary particle runtime attributes in parser function?
• Runtime call: “register variables”
• output: plotfile/openPMD 2D field

[RevathiJambunathan]

Thank you @hklion for volunteering to take this on

[ax3l]

@hklion updated me that she has currently no time to work on this. We'll check for a volunteer next dev meeting.

[PhilMiller]

We at Modern Electron just discussed yesterday that something exactly like this would be helpful in debugging https://github.com/ECP-WarpX/WarpX/issues/3215 - we'd plot density as a function of (x position, velocity/momentum) to test the hypothesis that it's the slowest-moving particles getting 'stuck' on numerical boundaries