[CAS bug, hang] Telescoping sums

08072017, 09:25 PM
(This post was last modified: 08112017 09:27 AM by ettlz.)
Post: #1




[CAS bug, hang] Telescoping sums
It appears HP Prime CAS 1.1.211 (fw 20170710, 12066) can't deal with simple telescoping sums, for example:
\[\sum_{n=1}^{\infty}\left(\frac1{n+1}\frac1n\right) \rightarrow \text{undef}\] This is a regression from the 50g. \[\sum_{n=1}^{a}\left(\frac1{n+1}\frac1n\right)\] returns \({\rm Psi}(1+a)+{\rm Psi}(2+a)1\) and this simplifies to the expected \(a/(1+a)\) (which the 50g returns immediately). Taking the limit \(a\rightarrow\infty\) works on the intermediate expression in terms of \({\rm Psi}\), but \[\lim_{a\rightarrow\infty}\sum_{n=1}^{a}\left(\frac1{n+1}\frac1n\right)\] hangs the Prime. The current Android app crashes. The summations works OK in Xcas 1.2.3, so I presume a fix is queued for the next firmware update. 

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