fix: handle r=0 in NFWSph deflections#430
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The analytic spherical NFW deflection divides by `eta = r/scale_radius` and evaluates `arccosh(1/r)` inside `coord_func_h`, both of which blow up to NaN at the profile centre. Any grid that included the origin pixel (e.g. an odd-sized image-plane grid centred on a lens at (0, 0)) propagated those NaNs through every subsequent ray-trace. Add a `xp.where(eta < 1e-6, ...)` guard so the centre pixel returns the symmetry-required value of zero, matching the existing 1e-6 / 1e-24 guards already used by the elliptical NFW path (`NFW.convergence_2d_from`, `NFW.shear_yx_2d_from`, `NFW.deflections_2d_via_analytic_from`). No public API change. Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
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Summary
NFWSph.deflections_2d_via_analytic_fromproduced NaN at the profile centre. The analytic form divides byeta = r/scale_radiusand evaluatesarccosh(1/r)insidecoord_func_h, both of which blow up at r=0.xp.where(eta < 1e-6, ...)guard so r=0 returns 0 (the symmetry-required value), matching the existing 1e-6 / 1e-24 guards already used by the ellipticalNFWpath (convergence_2d_from,shear_yx_2d_from,deflections_2d_via_analytic_from). No public API change.Why now
Surfaced by two scripts in
autolens_workspace/scripts/imaging/features/advanced/mass_stellar_dark/(fit.py,likelihood_function.py) where a manual stellar + dark + shear deflection sum is compared against theTracer's total. Both sides got NaN at the origin pixel, andnp.allclose(NaN, NaN) == Falsemade the comparison fail despite the math being correct everywhere else.API Changes
None.
NFWSph.deflections_yx_2d_from(grid)signature and return type unchanged; only the behaviour at r=0 changes (NaN → 0).Test plan
pytest test_autogalaxy/profiles/mass/dark/test_nfw.py— 25 passedNaN in dark/sum/lens == 0,allclose(sum, lens) == True,allclose(grid_manual, grid_tracer) == True, origin deflection now[-0., 0.]mass_stellar_darkworkspace scripts run end-to-end with noRuntimeWarning: divide by zeroand noAssertionError🤖 Generated with Claude Code