Stack overflow integrating csch(29/10 + 13/10 x)^3 (17/10 + 23/10 sech(29/10 + 13/10 x)^2)^3: the power-of-a-quadratic reduction recurses on a remainder the division did not reduce

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#1,373 opened on Sep 16, 2026 0 comments 0 reactions 0 assignees View on GitHub

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Assessment

Difficulty: 4/5
Estimated time: 3-5 days
Newbie friendliness: 48/100

Issue type: Bug
Clarity: Mostly clear
Activity status: Active
Tech stack: csharp
Domain: backend

Research direction

Start with IntegralPatterns.IntegrateRationalOverPowerOfQuadratic and TheFirstPowerCancels' Gather, reproducing the supplied integrand with rational parameters. Inspect the PolynomialLongDivision remainder checks at both recursion sites; done means the reduction declines when the remainder still has a higher variable power and the integrator returns a bounded decline instead of overflowing the stack.

Written by the indexing model from the issue text.

Description

Bug

csch(29/10+13/10*x)^3*(17/10+23/10*sech(29/10+13/10*x)^2)^3 (Rubi 6.5.7:30 with the parameters pinned to rationals) takes the process down with a stack overflow on master (01fa27bb), in IntegralPatterns.IntegrateRationalOverPowerOfQuadratic and, once that is guarded, in TheFirstPowerCancels' Gather: both divide the numerator by the quadratic with PolynomialLongDivision and recurse on the remainder at the same power, and for this integrand under u = e^x the division comes back with a remainder that is not linear, so the recursion never descends.

Fix in the PR that found it: a remainder that still has the variable to a higher power declines the reduction at both sites (the same problem then goes on to a decline within the budget rather than a crash). Why the division reports a remainder of full degree for these coefficients is not yet looked at.

Dominant language: C#
Stars: 832
Forks: 79
Avg merge: 3h 11m
Merged PRs (30d): 357

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