assumption, supposition?
- 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-