MathGroup Archive 2001

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Assumptions about variables

  • To: mathgroup at
  • Subject: [mg30727] Assumptions about variables
  • From: "Jacek Dziedzic" <dust at>
  • Date: Sat, 8 Sep 2001 02:56:13 -0400 (EDT)
  • Sender: owner-wri-mathgroup at

Hello all!

Can someone please tell me how do I tell mathematica (3.0) to assume certain
things about variables, for example that they are positive or are contained
in a range such as <3,4). In Derive you could declare a variable as
"positive" and it was very easy. The only thing I found out until now is how
to let it know that a variable is real, I do it like this:
a /: Im[a] = 0 (for a variable a).

Things like a /: Sign[a] = 1 don't do what I want.

As an example I have a partial differential equation that has a soliton
solution only when a parameter is positive. How do I tell the mathematica to
assume that this parameter must be positive?

Thanks in advance.

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