Re: NSum bug or am I doing something wrong?
- To: mathgroup at smc.vnet.net
- Subject: [mg93888] Re: [mg93869] NSum bug or am I doing something wrong?
- From: Bob Hanlon <hanlonr at cox.net>
- Date: Fri, 28 Nov 2008 05:05:04 -0500 (EST)
- Reply-to: hanlonr at cox.net
It is numerical noise, just use Chop.
NSum[(-1)^(k + 1)*(0.2)^k, {k, 1, 32}]
0.166667 + 1.1972*^-44*I
Sum[(-1)^(k + 1)*(0.2)^k, {k, 1, 32}]
0.166667
Sum[(-1)^(k + 1)*(2/10)^k, {k, 1, 32}] // N
0.166667
NSum[(-1)^(k + 1)*(.2)^k, {k, 1, 32}] // Chop
0.166667
Bob Hanlon
---- Ebpr Preb <ebpr08 at gmail.com> wrote:
=============
Hi,
I'm getting imaginary answers for simple NSums of rational numbers. The
example below produces the issue in Mathematica 7:
NSum[(-1)^(k + 1)*(.2)^k, {k, 1, 32}]
gives me the result:
0.166667 + 1.1972*10^-44 I
When I switch to Sum the problem disappears.
Any hint?
Thanks so much.
ebpr
--
Bob Hanlon