Initial-state matching and pressure realizability in counter-streaming electron-fluid comparisons
This diagnostic comment examines initial-state matching and pressure realizability in arXiv:2607.07106v1. Its exact mixture identities are correct. However, archived PIC and fluid initial moment-current profiles differ by $9.87\%$ in the full-domain, $x$-averaged relative $\ell^2$ norm; local Cartesian covariance pressures differ by about $20\%$ in $P_{xx}$ and $38.4\%$ in $P_{zz}$. The PIC input specifies proper momentum where the fluid input specifies ordinary velocity. Complete archive checks and independent ten-moment layout validation corroborate the data audit. Four clean-source fluid cases attempt comparisons of the posted and aggregate-PIC-matched initializations, while distinguishing the unavailable historical dirty build. At identical one-fluid endpoint times, matching lowers $P_{xx}$ error against PIC from $36.29\%$ to $28.85\%$, with smaller errors in density, current and $P_{zz}$ as well. These are numerical endpoint results, not validated physical dynamics: both one-fluid cases contain indefinite covariance tensors at saved intermediate times, and the clean unmatched two-fluid endpoint is also inadmissible. The matched two-fluid run terminates with an invariant-check assertion before producing its comparison endpoint. The clean implementation tests coordinate pressures without testing full tensor positivity. The original archived endpoints pass the same covariance checks; their intermediate trajectories and exact executable remain unidentified. A conditional loader calculation, an auxiliary homogeneous stability benchmark, a continuity clarification and a cancellation-conditioned heat-flux bound provide separate diagnostics. The results motivate matched moments and realizability checks without disproving the source’s exact algebra or establishing that its nonlinear physical conclusions are false.