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Leave a sum beside its own derivative to the plain substitution - #1943
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Rafael-SOWNet merged 1 commit intoOct 19, 2026
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Taking a power of x out of a fractional power of a sum (#1705) runs before `SolveBySubstitution`, and on `(x - 3 sqrt(x))^(2/3) (2 sqrt(x) - 3)/sqrt(x)` it took the integral somewhere it could not finish, where u = the sum answers it outright: 2.5.0 did in a fifth of a second, 2.6.0 not in twenty. The rule now passes over a sum when the rest of the integrand is a constant times that sum's derivative, checked at three sample points. Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_012sonx8iAspMiwRwokT1Ura
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2.6.0 lost
∫ (x - 3 sqrt(x))^(2/3) (2 sqrt(x) - 3)/sqrt(x) dx(Rubi 1.3.2, row 1130). 2.5.0 answered it in about 200 ms; 2.6.0 does not answer it within 20 s. Bisected to #1705. Its rule, which takes a power of x out of a fractional power of a sum, runs beforeSolveBySubstitution. On this integrand the rule sends the search somewhere it cannot finish, whereas u = the sum answers it outright.The rule now skips a sum when the rest of the integrand is a constant times that sum's derivative. It checks this as a constant ratio at three sample points, with the symbols pinned. #1705's own examples are unaffected, because their rest is not such a multiple.
Measured
These runs compare against master da06bac. Each one is in a separate process.
The one row that moved, 1.3.2:1130, was re-run alone. It timed out on master and is solved in 374 ms on this branch.
The performance gate passed. The unit suite passed: 15,580 tests, 0 failed.
The new test,
ASumBesideItsDerivativeKeepsItsPowerOfXIntegralTest, covers the regression and one of #1705's shapes, at six points.No BREAKING-CHANGES entry is needed: this restores an answer 2.5.0 gave.
🤖 Generated with Claude Code
https://claude.ai/code/session_012sonx8iAspMiwRwokT1Ura