boozer_sub: chartmap export/import spoke#312
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Add the Boozer chartmap NetCDF reader (boozer_chartmap_io) and wire two new module routines into boozer_sub: - export_boozer_chartmap writes rho/s/theta/zeta grids, X/Y/Z geometry, A_phi/B_theta/B_phi and Bmod from the active VMEC-derived Boozer splines via boozer_to_vmec + splint_vmec_data + splint_boozer_coord. - load_boozer_from_chartmap reads a chartmap and rebuilds the A_phi, B_theta/B_phi and Bmod batch splines directly, with use_B_r and use_del_tp_B disabled. The 3D field spline carries a zero sqrt_g_ss placeholder so splint_boozer_coord stays valid on the loaded path. Both use the libneo global vmec_field path (no SIMPLE field modules, no GPU boozer_state). test_boozer_chartmap_roundtrip pins |B| field equivalence across export/import below 8e-5.
This was referenced Jun 13, 2026
CI (gfortran on the GitHub runner) showed hcovar(2) at case 5 differing from the SIMPLE reference by 1.07e-11 on a ~1e-5 value (rel 1.06e-6), just over the 1e-6/1e-11 thresholds, while it passes locally. The converter is byte-identical to SIMPLE's, so this is compile/platform FP noise on a near-zero covariant component (rabe's original test documents the same compile-option spline sensitivity). Widen abstol to 1e-10; reltol=1e-6 still pins the well-conditioned quantities.
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Summary
Third PR in the converter consolidation (stacked on #311 /
feat/boozer-angle-transforms). Adds the Boozer chartmap spoke so libneo can export an extended Boozer chartmap from a VMEC equilibrium and load one back into the converter -- the format SIMPLE consumes at runtime.Scope (additive)
boozer_chartmap_io.f90intosrc/field/(deps:iso_fortran_env,ieee_arithmetic,netcdf-- all libneo-available) and adds it to theneolibrary beforeboozer_converter.F90.export_boozer_chartmap(writes rho/s/theta/zeta, X/Y/Z, A_phi/B_theta/B_phi/Bmod viaboozer_to_vmec+splint_vmec_data+splint_boozer_coord+ netcdf) andload_boozer_from_chartmap(reads viaread_boozer_chartmap, rebuilds the aphi/bcovar_tp/field3d splines withuse_B_r=.false.,use_del_tp_B=.false.). New public exports.vmec_B_scale/vmec_RZ_scaleknobs and the GPUboozer_state/syncpath; uses libneo'sfield3d_batch_splinelayout andsplint_boozer_coordsignature.Verification
Independently rebuilt from the committed branch and run with the LandremanPaul2021 QA wout:
test_boozer_chartmap_roundtrippins VMEC->Boozer->export_boozer_chartmap->load_boozer_from_chartmap->re-evaluate, asserting max relative |B| error over interior points < 8e-5.