Introducing new variables implicitly

Asked Oct 31 '13 at 19:01

Active Nov 01 '13 at 01:46

Viewed 149 times

I have a calculation

expr111 = cs[giso, xiso, 1, 1, 1]

that gives the result

-((k x)/(2 (1 + 1/4 k (x^2 + y^2 + z^2))))

I also have two other expressions:

fx = -((k rho^2 x)/(1 + 1/4 k (x^2 + y^2 + z^2))^3)
ff = rho^2/(1 + 1/4 k (x^2 + y^2 + z^2))^2

Pretty obviously expr111 == fx/(2 ff). How do I get Mathematica to make this substitution?

edited Nov 01 '13 at 01:46

m_goldberg

asked Oct 31 '13 at 19:01

John

1

Related: Can I simplify an expression into form which uses my own definitions? – ssch Oct 31 '13 at 19:12
Are you asking, given your definitions, can you get Mathematica to give fx/ff/2 when you evaluate exp111? That's 180 degrees out of phase with Mathematica normal evaluation rules. – m_goldberg Nov 01 '13 at 01:38
this is also very relevant. It works here but you need to transform your fractions to polynomials first (assuming your denominators are non-zero) – gpap Nov 01 '13 at 10:48
This question appears to be off-topic because it makes no sense when considered in the context of Mathematica's evaluation rules. – m_goldberg Nov 01 '13 at 12:31
@m_goldberg I was imagining a result like Hold[fx/(2 ff)] – ssch Nov 01 '13 at 13:16

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