16
$\begingroup$

Bug introduced in 9.0.1 and fixed in 10.0.0


Consider

RSolve[{a[n + 1] == 2 a[n] + n (1 + 2^n), a[1] == 1}, a[n], n]

Mathematica 8 can solve this quickly, but Mathematica 9, even after being allowed to run for a long time, cannot give a result.

$\endgroup$
  • 5
    $\begingroup$ Strange, but this works : RSolve[{a[n + 1] == 2 a[n] + b[n], a[1] == 1}, a[n], n] /. b[m_] -> m (1 + 2^m). $\endgroup$ – b.gates.you.know.what May 1 '14 at 5:07
  • 2
    $\begingroup$ I can confirm this behavior and think it is a bug. I have sent WRI tech support a report of this problem. I will post their answer when I receive it. $\endgroup$ – m_goldberg May 1 '14 at 6:32
  • 5
    $\begingroup$ @m_goldberg C'mon! It's clearly a feature! $\endgroup$ – Dr. belisarius May 1 '14 at 7:27
  • $\begingroup$ Sometimes internal functionality gets improved by making it more flexible, but in the course of doing so a good hard-coded algorithm that solves a specific problem gets broken. $\endgroup$ – Tyler Durden Mar 12 '16 at 16:35
3
$\begingroup$

I submitted a report about this problem to WRI tech support. I have received their reply and quote it part below.

Thank you for bringing this RSolve issue to our attention.

I can reproduce the situation you found on both Mathematica 9 and Mathematica prerelease and have filed a report on it.

I think it is safe to tag this question with .

$\endgroup$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.