Re: Ask Mathematica to sub for a long expression
- To: mathgroup at smc.vnet.net
- Subject: [mg71878] Re: Ask Mathematica to sub for a long expression
- From: Jean-Marc Gulliet <jeanmarc.gulliet at gmail.com>
- Date: Sat, 2 Dec 2006 05:10:44 -0500 (EST)
- Organization: The Open University, Milton Keynes, UK
- References: <ekp4o4$2fq$1@smc.vnet.net>
aaronfude at gmail.com wrote: > Hi, > > Is it possible to ask Mathematica to replace a long expression, such as > Sqrt[a^2+b^2-2*a*b*Cos[theta]] with "c", whenever it encounters that > long expression? > > Thanks! > > Aaron Fude > Use transformation rules [1]. For example, f = 3*Sqrt[a^2 + b^2 - 2*a*b*Cos[\[Theta]]]; f /. Sqrt[a^2 + b^2 - 2*a*b*Cos[\[Theta]]] -> c --> 3*c f = 3*Sqrt[a^2 + b^2 - 2*a*b*Cos[\[Theta]]] + 1/Sqrt[a^2 + b^2 - 2*a*b*Cos[\[Theta]]]; Together[f /. a^2 + b^2 - 2*a*b*Cos[\[Theta]] -> c] --> (1 + 3*c)/Sqrt[c] Regards, Jean-Marc 1. _The Mathematica Book_, /Section 2.5: Transformation Rules and Definitions/, http://documents.wolfram.com/mathematica/book/section-2.5