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Re: how to find n in expression x^n using a pattern?
*To*: mathgroup at smc.vnet.net
*Subject*: [mg58496] Re: [mg58426] how to find n in expression x^n using a pattern?
*From*: stephen layland <layland at wolfram.com>
*Date*: Mon, 4 Jul 2005 02:24:28 -0400 (EDT)
*Mail-followup-to*: steve <nma124@hotmail.com>, mathgroup@smc.vnet.net
*References*: <200507020806.EAA01589@smc.vnet.net>
*Sender*: owner-wri-mathgroup at wolfram.com
and thus spake steve [2005.07.02 @ 04:08]:
> I am learning patterns in Mathemtica, and I thought this will be easy.
>
> suppose you are given a factored expression, such as x^n(x^2+2)(x^3+4)
> where 'n' above can be any number, including zero (i.e. there is no
> (x) as a separate factor). I need to find 'n', which can be
> 0,1,2,3,..etc..
>
> i.e I need to find the power of the factor x by itself if it exist in
> the expression. not (x^n+anything), just (x^n) byitself.
>
> For example
>
> p= x (x^2+2) ---> here n=1
Here' ssomething that might work for you:
(Exponent[Cases[p, x | x^n_], x] /. {} -> {0})[[1]]
It's kind of ugly, but like someone suggested before, first we use
cases to find any occurance of x or x^n_ by itself in the multiplication
expression. We then use the function Exponent to turn the x^n_ or x
into n or 1. Lastly, we explicitly set the exponent to 0 if we didn't find
anything, and get rid of the list enclosure.
I'm sure there are other methods, however.
Happy hacking!
--
/*------------------------------*\
| stephen layland |
| Documentation Programmer |
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