       Re: smart change of variables?

• To: mathgroup at smc.vnet.net
• Subject: [mg87713] Re: smart change of variables?
• From: dh <dh at metrohm.ch>
• Date: Wed, 16 Apr 2008 05:01:07 -0400 (EDT)
• References: <fu21bk\$rb6\$1@smc.vnet.net>

```
Sorry , just made a type. Here is the correct code:

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}]

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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