Skip to content

Two proportional linears are not divided by their zero determinant - #1777

Merged
Rafael-SOWNet merged 1 commit into
masterfrom
proportional-linears-are-not-divided-by-their-zero-determinant
Oct 5, 2026
Merged

Rafael-SOWNet merged 1 commit into
masterfrom
proportional-linears-are-not-divided-by-their-zero-determinant

Conversation

@Rafael-SOWNet

Copy link
Copy Markdown
Member

Closes #1776.

(a + b x)^(-3)/sqrt(c a + c b x) was answered on master with an expression that divides by b a c - a b c, which is zero, so it has no value at any point:

integrand 2.5.0 master 4105b3bf this
(a + b x)^(-3)/sqrt(c a + c b x) declined no value anywhere -2/(5 b) (a + b x)^(-2) (c a + c b x)^(-1/2)
1/(c (a + b x)^3)^(3/2), Rubi's 1.1.3.2:3412 declined no value anywhere -2/(7 b c) sgn(a + b x) (c (a + b x))^(-1/2) (a + b x)^(-3)
1/(c (a + b x)^3)^(5/2), 1.1.3.2:3413 declined no value anywhere -2/(13 b c) sgn(a + b x) (c (a + b x))^(-3/2) (a + b x)^(-5)

Each answer is differentiated back and compared with the integrand on both sides of the root of a + b x.

What changes. The recurrence #1758 added for a negative power of one linear beside a power of another divides by the two linears' determinant D = b c' - a d', and declined where D was zero as written. Beside a multiple of the same linear it is zero only once the products in it are sorted. It is decided as a value now, with PartialFractions.IsZeroAsAValue, and the integrand is left to the rules that answered it before #1758; the rule for two linears beside each other already declines proportional ones, by AreProportionalAtSampledPoints.

Tests: LinearPowerRecurrenceIntegralTest.BesideAMultipleOfTheSameLinear, the three rows above, differentiated back at points on both sides of the root; master answers each with no value.

Measured: the calculus and corpus tests pass on the head, and the library builds for netstandard2.0. The change only declines where the determinant is zero as a value, which leaves the integrand to the rules before it.

🤖 Generated with Claude Code

https://claude.ai/code/session_012sonx8iAspMiwRwokT1Ura

The recurrence for a negative power of one linear beside a power of another
divides by the two linears' determinant, and declined where it was zero as
written. Beside a multiple of the same linear, a + b x beside c a + c b x, it
is b a c - a b c, zero only once its products are sorted, and the answer had
no value anywhere. It is decided as a value now, and the integrand is left to
the rules that answered it before the recurrence was added.

Closes #1776.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_012sonx8iAspMiwRwokT1Ura
@Rafael-SOWNet Rafael-SOWNet added this to the 2.6.0 milestone Oct 5, 2026
@Rafael-SOWNet
Rafael-SOWNet merged commit 9f987f3 into master Oct 5, 2026
34 checks passed
Sign up for free to join this conversation on GitHub. Already have an account? Sign in to comment

Labels

None yet

Projects

None yet

Development

Successfully merging this pull request may close these issues.

A negative power of a linear beside a root of a multiple of it is integrated as an expression with no value

1 participant