Re: New version, new bugs
- To: mathgroup at smc.vnet.net
- Subject: [mg43205] Re: New version, new bugs
- From: Paul Abbott <paul at physics.uwa.edu.au>
- Date: Wed, 20 Aug 2003 22:24:50 -0400 (EDT)
- Organization: The University of Western Australia
- References: <bgq9q4$d50$1@smc.vnet.net> <bhaah2$kt6$1@smc.vnet.net>
- Sender: owner-wri-mathgroup at wolfram.com
In article <bhaah2$kt6$1 at smc.vnet.net>, Maxim <dontsendhere@.> wrote:
> 1) when writing out sums of rising factorials:
>
> In[1]:=
> Module[
> {c = Pochhammer[-2, -1 + k]},
> Sum[c,{k,1,Infinity}]
> ]
>
> Out[1]=
> Infinity*Pochhammer[-2, -1 + k]
>
> in version 4.2 this sum is left unevaluated -- hardly an improvement;
Because Sum does not evaluate its arguments (it is HoldAll), Evaluate is
required:
Module[
{c = Pochhammer[-2, -1 + k]},
Sum[Evaluate[c],{k,1,Infinity}]
]
You can avoid such a convoluted construct by writing
Sum[Pochhammer[-2, k - 1], {k, 1, Infinity}]
> 3) at first I was scanning the lists of coefficients in a more procedural
> way, and noticed a strange behaviour or Increment; here's an example to
> demonstrate it more clearly:
>
> In[1]:=
> Compile[
> {},
> Module[
> {L={10,20,30},a=1},
> L[[a++]]++;
> Append[L,a]
> ]
> ][]
>
> Out[1]=
> {10,31,30,4}
>
> Imagine using a C compiler with this sort of glitches. Once again the bug
> appears in a function that doesn't have a precise definition; all this
> certainly would have been of little importance for an educational software,
> but not for a serious development tool.
Perhaps a previous posting to this group (in 1999),
http://groups.google.com/groups?q=%2B%2B+withoff+increment&hl=en&lr=&ie=U
TF-8&selm=7n68mn%24gu3%40smc.vnet.net&rnum=2
explains your problem here?
Cheers,
Paul
--
Paul Abbott Phone: +61 8 9380 2734
School of Physics, M013 Fax: +61 8 9380 1014
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