imposing parameter assumptions

*To*: mathgroup at smc.vnet.net*Subject*: [mg44184] imposing parameter assumptions*From*: "drr7" <rondeau at uvic.ca>*Date*: Sat, 25 Oct 2003 06:26:39 -0400 (EDT)*Organization*: University of Victoria*Sender*: owner-wri-mathgroup at wolfram.com

Simple question: How do I impose assumptions on the sign of parameters in symbolic equations and then test for the sign of an expression. Example: suppose I want to test the sign of f[a]=a^-3 if a<0. I tried combinations of Refine and Positive, but that does not seem to work for me. What I am really trying to do is sign a long expression for a derivative. Thanks.

**Follow-Ups**:**Re: imposing parameter assumptions***From:*"Peter Pein" <nospam@spam.no>