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Re: imposing parameter assumptions


Use Simplify

f[a]=a^-3;

Simplify[#[f[a]], a<0]& /@ 
  {Sign, Positive, Negative, NonNegative}

{-1,False,True,False}


Bob Hanlon

In article <bndkco$g6f$1 at smc.vnet.net>, "drr7" <rondeau at uvic.ca> wrote:

<< 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.
 >><BR><BR>


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