boozer_sub: VMEC<->Boozer angle transforms#311
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Port the angle-transform machinery from the SIMPLE converter into libneo's boozer_sub: delthe_delphi_BV, vmec_to_boozer, and the Newton inverse boozer_to_vmec. compute_boozer_data now fills delt_delp_V_grid (theta_B-theta_V and phi_B-phi_V on the VMEC-angle grid) unconditionally and delt_delp_B_grid on the Boozer-angle grid behind use_del_tp_B. build_boozer_delt_delp_batch_splines constructs the descriptors. Existing splint outputs and perqua rows are unchanged. Add test_boozer_angle_roundtrip pinning round-trip invertibility of the forward and inverse transforms.
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
Second PR in the hub-and-spoke converter consolidation (stacked on #310). Ports SIMPLE's VMEC<->Boozer angle-transform machinery into libneo's
boozer_sub, so the converter can map between VMEC and Boozer angles in both directions. The chartmap export spoke (next PR) needsboozer_to_vmec.Scope (additive)
delt_delp_V_grid/delt_delp_B_gridarrays +delt_delp_V/Bbatch-spline descriptors and ready flags (libneosavestyle, not SIMPLE's GPU/allocatable path).delthe_delphi_BV,vmec_to_boozer,boozer_to_vmec(Newton, niter=100, epserr=1e-14),build_boozer_delt_delp_batch_splines(called fromget_boozer_coordinates_impl, freed inreset_boozer_batch_splines).compute_boozer_datafills the V grid unconditionally (needed by the forward/backward maps) and the Boozer-angle B grid only whenuse_del_tp_B(default.false.). Existing perqua rows, splint outputs and numeric behavior are unchanged.vmec_to_boozer,boozer_to_vmec,delthe_delphi_BV.vmec_field; no SIMPLEfield/vmec_field_eval/GPUboozer_stateintroduced.Verification
Independently rebuilt from the committed branch and run with the LandremanPaul2021 QA wout:
test_boozer_converter_vs_simple) stays green: behavior is byte-unchanged.test_boozer_angle_roundtrippins invertibility (a previously-untested gap):vmec_to_boozerthenboozer_to_vmecrecovers(theta, varphi)to < 1e-10 (modulo periodicity), and the reverse, at s in {0.2, 0.5, 0.8} for several angle pairs.