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+--- Thread: Infinite sum wrong result. Bug in Giac? (/thread-2723.html)
Infinite sum wrong result. Bug in Giac? - danielmewes - 12-29-2014 01:55 AM
Hi all,
I was reading this bug report for the 50g http://bugs.hpcalc.org/show_bug.cgi?id=238 and entered the same sum into the Prime for testing:
sum from k=1 to infinity (((1+i)/2)^k)
the Prime gives me 0 as the result.
CAS mode, Settings: Exact on, Complex off (turning it on doesn't change the result), Use sqrt on, Use i on.
I can also reproduce this in Giac/Xcas:
`sum(((1+i)/2)^k, k=1...+infinity)`
gives me 0 as well.
In contrast, WolframAlpha says the result is i
http://www.wolframalpha.com/input/?i=sum+%28%28%281%2Bi%29%2F2%29^k%29%2C+k%3D1+to+infinity
Trying a few finite upper boundaries on the Prime suggests that Wolfram Alpha is correct, and Giac/Prime are wrong.
RE: Infinite sum wrong result. Bug in Giac? - danielmewes - 12-29-2014 01:58 AM
Versions:
HP Prime 2014 12 3 (6975)
xcas 1.1.3
RE: Infinite sum wrong result. Bug in Giac? - Helge Gabert - 12-29-2014 02:49 AM
Confirmed.
And, by the same token, sum from k=1 to infinity (((1-i)/2)^k) should return -i, but the Prime also thinks it is zero.
[Edit: Also checked sum from k=1 to infinity (((-1+i)/2)^k) should return -2/5+i/5, but the Prime returns -2/5.
Ditto sum from k=1 to infinity (((-1-i)/2)^k) should return -2/5-i/5, but the Prime returns -2/5 only.]
RE: Infinite sum wrong result. Bug in Giac? - parisse - 12-29-2014 09:20 AM
Fixed in source, thanks.
RE: Infinite sum wrong result. Bug in Giac? - danielmewes - 12-30-2014 04:07 AM
Thanks for the super quick fix Bernard!
Let's see when we get it for the Prime...