how to initialize long velocity perturbation expressions

[yanghf263]

I am running a Hybrid-PIC turbulence setup, and I need to impose an initial ion velocity perturbation.

I am currently trying two approaches:

1. Analytic parser approach (momentum_expressions)

   • I build a multi-mode perturbation expression for ux, uz.
   • When the expression becomes long (many modes), the run appears to hang/fail during parsing.
   • It seems related to parser/string length limits.

2. Direct memory injection approach (NumPy)

   • After initialize_warpx(), I directly modify particle ux, uz arrays tile-by-tile.
   • Injection itself succeeds, but the step=0 plotfile diagnostics (including particle-derived fields like vx, vx2) do not include the injected perturbation.

Questions

1. Is there a recommended way to bypass parser limits for long analytic expressions (chunking, external table/function, parser options, etc.)?
2. If using direct memory injection, can step=0 diagnostics include the injected perturbation?
   • If yes, what is the correct callback/output order or API pattern to force a post-injection step=0 snapshot?

Thanks!