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 >