Replace GSL quadrature and Levin sum in hyper1F1 with fortnum (2/5) - #30
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Replace GSL quadrature and Levin sum in hyper1F1 with fortnum (2/5)#30krystophny wants to merge 5 commits into
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Drop the gsl_sf_bessel_In_array C binding in mephit_pert and compute the
modified Bessel functions through fortnum's bessel_in_array. fortnum fills
I_0..I_nmax in one pass, so the orders |m|-1, |m|, |m|+1 are recovered with
the symmetry I_{-n}(x) = I_n(x); for pol_mode = 0 the order -1 maps to I_1.
Wire fortnum via CMake FetchContent at the pinned tag, guarded so a build that
also pulls fortnum transitively through libneo does not declare the target
twice. Add the fortnum include directory for the C/C++ sources and link the
fortnum target. GSL stays linked until the remaining call sites move over.
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Route the a = 1 confluent hypergeometric evaluation through the fortnum C ABI: the boundary integral uses fortnum_integrate_qag with the Gauss-Kronrod 21 rule, and the Kummer-series acceleration uses fortnum_levin_u_accel. Both fortnum routines take the integrand plus an opaque context, so the existing quad_params struct is forwarded unchanged and no workspace is allocated. Add float.h for DBL_EPSILON, which was previously pulled in transitively through a GSL header.
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Merge order
Stack sequence: #29 -> #30 -> #31 -> #32 -> #33.
Each PR is now based on main individually, so its diff is cumulative against main and shares code with its stack neighbors. Merge in the sequence above. Once a predecessor merges into main, the next PR rebases onto it and its diff shrinks to its own increment.
Second in the fortnum migration stack (base: the Bessel PR). Moves the C confluent-hypergeometric evaluation off GSL.
Dependency removed: GSL adaptive quadrature and Levin u-sum acceleration in src/hyper1F1.c (gsl_integration_qag, gsl_integration_workspace, gsl_set_error_handler_off, gsl_sum_levin_u_*). The boundary integral now uses fortnum_integrate_qag with the Gauss-Kronrod 21 rule, and the Kummer-series acceleration uses fortnum_levin_u_accel. Both fortnum routines take the integrand plus an opaque context, so the existing quad_params struct is forwarded unchanged and no workspace is allocated. float.h is added for DBL_EPSILON, which was previously pulled in transitively through a GSL header.
Verification
Build the shared library at this tip:
No GSL integration or sum symbols remain undefined; fortnum's routines are defined in the library:
The only GSL symbols still referenced belong to the C call sites moved in PR 3 of this stack (glfixed, gsl_strerror). As in PR 1, the .x executables link only after PR 4 removes the empty FFTW link.
Note: fortnum pin updated to current main (92de6e9) after a fortnum history rewrite; old shas no longer resolve.