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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

> 




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