Re: assumption, supposition?
- To: mathgroup at smc.vnet.net
- Subject: [mg15500] Re: assumption, supposition?
- From: "Dale Horton" <daleh>
- Date: Mon, 18 Jan 1999 04:22:49 -0500
- Organization: Wolfram Research, Inc.
- References: <firstname.lastname@example.org>
- Sender: owner-wri-mathgroup at wolfram.com
Another method is to use PowerExpand. In:= PowerExpand[Sqrt[x^2]] Out= x -Dale Erk Jensen wrote in message <774kr1$46h at smc.vnet.net>... >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- >