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Re: How to separate a sum into terms
*To*: mathgroup at smc.vnet.net
*Subject*: [mg92055] Re: How to separate a sum into terms
*From*: "David Park" <djmpark at comcast.net>
*Date*: Thu, 18 Sep 2008 06:17:37 -0400 (EDT)
*References*: <gaqf4g$doa$1@smc.vnet.net>
Here is your expression:
expr = (a + b - c + f[1] - g[a]/g[b]);
The Head of the expression is:
Head[expr]
Plus
But you would like to have a List instead of a sum (Plus) of the items. Do
this by applying List to the expression. This replaces the Head, Plus, by a
new Head, List.
Apply[List, expr]
{a, b, -c, f[1], -(g[a]/g[b])}
Or use the Mathematica shortcut, @@, for Apply:
List @@ expr
{a, b, -c, f[1], -(g[a]/g[b])}
Or Apply directly to the expression:
List @@ (a + b - c + f[1] - g[a]/g[b])
{a, b, -c, f[1], -(g[a]/g[b])}
In this particular case you could also do a simple substitution:
a + b - c + f[1] - g[a]/g[b] /. Plus -> List
{a, b, -c, f[1], -(g[a]/g[b])}
But that would not work if, for example, g had a sum for an argument. So
Apply is the best method.
--
David Park
djmpark at comcast.net
http://home.comcast.net/~djmpark/
"Slava Rychkov" <slava.rychkov at gmail.com> wrote in message
news:gaqf4g$doa$1 at smc.vnet.net...
> Hi!
>
> I want to separate a Mathematica expression written as a sum into
> separate terms
> E.g. for
>
> a+b-c+f[1]-g[a]/g[b]
>
> I want to get a list
>
> {a,b,-c,f[1],-g[a]/g[b]}
>
> Is there a simple way to do this?
>
> Thanks,
> --
> Vyacheslav Rychkov https://mail.sns.it/~rychkov
> Scuola Normale Superiore Tel: +39-050-509068 (office)
> Classe di Scienze +39-050-3820086 (home)
> Piazza dei Cavalieri, 7 +39-3403925168 (mobile)
> 56100 Pisa Fax: +39-050-509045
> Italy E-mail: Rychkov at sns.it
>
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