- To: mathgroup at smc.vnet.net
- Subject: [mg15331] assumption, supposition?
- From: Erk Jensen <Erk.Jensen at cern.ch>
- Date: Fri, 8 Jan 1999 04:15:20 -0500
- Sender: owner-wri-mathgroup at wolfram.com
Probably I'm looking up the wrong keyword in Mathematica help, but I can't find what I'm looking for. Maybe that's because I've learned those expressions in german... My problem: I want Mathematica to assume that a certain condition is satisfied for the following algebraic transformations. More specifically: Let rho describe a radius coordinate. I know it is not negative real. So, for transformations of expressions containing rho, e.g. Sqrt[rho^2], I want assure Mathematica that 0 <= rho is in fact satisfied, and that it is consequently allowed to replace Sqrt[rho^2] by rho. How do I do that? My solution was Unprotect[Sqrt]; Sqrt[rho_^2] := rho/; 0 <= rho; Protect[Sqrt]; rho /: 0 <= rho = True; and this seems to work, but I wonder whether this is really the proper way. Since the TagSet I'm using here assigns the whole statement to rho, and ?rho results in Global`rho rho /: 0 <= rho = True so I still have my doubts ... Can some of you experts enlighten me? Thanks in advance -erk-