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Integrate a power of a quotient of linears beside whole powers of them - #1953

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Oct 19, 2026
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Part of #233.

e^(n acoth(a x))/(c - a^2 c x^2)^m was declined for m = 2, 3 and 4. The fold rule writes e^(n acoth(a x)) as ((a x + 1)/(a x - 1))^(n/2). Under the Moebius substitution t = (p + q x)/(r + s x) we have p + q x = t (r + s x), r + s x = D/(q - s t) and dx = D/(q - s t)^2 dt. So t^alpha (p + q x)^j (r + s x)^k dx becomes D^(j + k + 1) t^(alpha + j) (q - s t)^(-(j + k + 2)) dt, a polynomial in t times a power of it wherever j + k <= -2. The new rule, SolveByTheMoebiusSubstitutionOfAQuotientOfLinears, does this. A whole power of a quadratic that is a multiple of the two linears' product counts as a power of each. Two scope limits:

  • the power of the quotient must not be whole, since a whole power makes a rational function, which belongs to the partial fractions;
  • a half-odd power of the quadratic is left alone, since it is not the product of the linears' powers on every side of their roots.

Measured against master 8a1ef454:

master this branch
7.3.6, 7.4.2 and 1.1.1.2, 3,613 rows 3,558 3,564
moves, each re-run alone 0 of 8 6 of 8, 0 wrong. These are 7.4.2:852-854, and three x^m rows (7.3.6:882 and 1448, 7.4.2:1037) whose radical substitution leaves such a power in the new variable. Their answers carry provided (1 + a x)/(1 - a x) >= 0
families 0 (whole) and 1 (40 a file), samples of 2–8 identical
performance gate passed
suite 15,601 passed, 0 failed

The atanh mirrors, answered since earlier in this cycle, now also come out under this substitution, written ((1 + a x)/(1 - a x))^(n/2 - 1) where they were (((1 + a x)/(1 - a x))^(1/2))^(n - 2). The two are equal for principal powers and about the same length. 2.5.0 declined them, so the entry in BREAKING-CHANGES.md counts them as new answers.

The rebase onto #1952 conflicted at the shared anchor. I resolved it by keeping both rules; the diff is the branch's own, and the tests of #1950–#1952 together with this one pass on the combined tree (27/27).

🤖 Generated with Claude Code

https://claude.ai/code/session_012sonx8iAspMiwRwokT1Ura

Under the Moebius substitution t = (p + q x)/(r + s x), p + q x = t (r + s x),
r + s x = D/(q - s t) and dx = D/(q - s t)^2 dt with D = q r - p s, so
t^alpha (p + q x)^j (r + s x)^k dx is D^(j + k + 1) t^(alpha + j)
(q - s t)^(-(j + k + 2)) dt: a polynomial in t times a power of it wherever
j + k <= -2. A whole power of a quadratic that is a multiple of the linears'
product counts as a power of each. e^(n acoth(a x)) arrives folded as
((a x + 1)/(a x - 1))^(n/2), and over (c - a^2 c x^2)^m it is that. Only for
a power of the quotient that is not whole: a whole one is a rational
function, the partial fractions'.

Rubi's 7.4.2: e^(n acoth(a x))/(c - a^2 c x^2)^m for m = 2, 3, 4, and three
x^m rows of 7.3.6 and 7.4.2 whose radical substitution leaves such a power
in the new variable, go from unevaluated or timed out to solved, 0 wrong.
Families 0 and 1 and samples of 2-8 otherwise identical; gate and suite
pass.

Part of #233.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_012sonx8iAspMiwRwokT1Ura
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