no answer (null) to limit 1/x + ln(x) #209

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1. MomoDeve

   added

   Minor bug

   on Sep 13, 2020
2. Happypig375 commented on Sep 13, 2020

   

   Happypig375

   on Sep 13, 2020

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   Hang?
3. MomoDeve

   changed the title [-]no answer to limit 1/x + ln(x)[/-] [+]no answer (null) to limit 1/x + ln(x)[/+] on Sep 13, 2020
4. WhiteBlackGoose

   added this to the 1.2.1 milestone on Sep 30, 2020
5. WhiteBlackGoose

   modified the milestones: 1.2.1, 1.2.2 on Oct 16, 2020
6. Happypig375

   closed this as completedon Aug 3, 2026
7. Happypig375

   reopened this on Aug 3, 2026
8. Happypig375

   added a commit that references this issue on Aug 4, 2026

   Do on the one-sided path what the two-sided one does (#697)

   ...

   ecd5759
9. Rafael-SOWNet commented on Aug 4, 2026

   

   Rafael-SOWNet

   on Aug 4, 2026

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   Fixed. Your literal case:

   LimitFunctional.ComputeLimit("1/x + ln(x)", "x", 0, ApproachFrom.Right)   // +oo

   which agrees with the Wolfram Alpha link.

   It took three changes rather than one, because the one-sided path turned out to be missing everything the two-sided path had rather than one thing:

   • Do on the one-sided path what the two-sided one does #697 — the four transformations in front of the descent ran only under BothSides, and behind the descent there was nothing at all, so a one-sided limit got neither the remarkable limits nor l'Hopital's rule. It also added the fallback that moves the destination out to infinity, which is what your case needs.
   • Put a difference of two divergent fractions over one denominator #699 — a difference of two divergent parts had no reading; over a common denominator it becomes an ordinary quotient.
   • Say which infinity a quotient with a vanishing divisor tends to #700 — a quotient whose divisor vanishes now says which infinity, by reading the side off the divisor's first non-vanishing derivative.

   Measured on a corpus of 72 one-sided limits worked out by hand: master answered 17 correctly, five of those being wrong answers rather than unanswered ones; with the three it is 64, none wrong. Worth stating that the failure mode was not only "no answer" — several came back as NaN, which asserts the limit does not exist.
10. Rafael-SOWNet

    closed this as completedon Aug 4, 2026
11. Happypig375

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12. Happypig375

    removed

    Minor bug

    on Sep 22, 2026