The Plot isoline `.value` checks asserted at WithinAbs(value, 1e-10), which
is platform-fragile: libm transcendentals (exp/log/pow) differ in the last
few bits across glibc, Apple libm, and UCRT, and that propagates through
the EOS solvers into ~1e-9 to 1e-10 relative differences in the computed
range bounds. Reference data regenerated on macOS in #2749 therefore broke
the Linux CI.
Switch to `WithinAbs(v, abs) || WithinRel(v, 1e-8)`: keeps the absolute
tolerance as a near-zero safety net and adds a 1e-8 relative tolerance
that comfortably covers the observed cross-platform jitter (worst case
~5e-9 rel for p_isolines[4]). Updated the generator script and re-ran it
to regenerate src/CoolPropPlot.cpp.
Co-authored-by: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
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