Re: smart change of variables?
- To: mathgroup at smc.vnet.net
- Subject: [mg87712] Re: smart change of variables?
- From: dh <dh at metrohm.ch>
- Date: Wed, 16 Apr 2008 05:00:55 -0400 (EDT)
- References: <fu21bk$rb6$1@smc.vnet.net>
Hi barrow,
you may achieve this using e.g. Solve:
Solve[{expr==(k1+2 k2) (p1+2
p2)p1+p2==k1+k2,s==(p1+p2)^2,t==(-k1+p1)^2,u==(-k2+p1)^2,},expr,{p1,p2,k1,k2}]
hope this helps, Daniel
Barrow wrote:
> Dear all,
>
> I have a arithmetic problem.
> I have an expression expr = (p1 + 2*p2)*(k1 + 2*k2)
> where p1 + p2 = k1 + k2
> I wanna make the following change of variables,
> s = (p1 + p2)^2
> t = (p1 - k1)^2
> u = (p1 - k2)^2
>
> Is it possible to tell Mathematica to express expr
> in terms of s, t, and u automatically?
>
> Thanks so much.
> any ideas would be appreciated.
> Sincerely Barrow
>