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MathGroup Archive 1997

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Fwd: Re[a]>0 ?

  • To: mathgroup at smc.vnet.net
  • Subject: [mg6240] Fwd: [mg6198] Re[a]>0 ?
  • From: BobHanlon at aol.com
  • Date: Fri, 28 Feb 1997 03:22:23 -0500
  • Sender: owner-wri-mathgroup at wolfram.com

Unprotect[Positive, Greater];
Positive[Re[a_?Positive]] = True;
(Re[a_?Positive] > 0) = True;
Protect[Positive, Greater];
a/: Positive[a] = True;

{Positive[a], Positive[Re[a]], Re[a] > 0}

{True,True,True}

Integrate[E^(-a*x^2), {x, -Infinity, Infinity}]

Sqrt[Pi]/Sqrt[a]
---------------------
Forwarded message:
From:	dreger at wam.umd.edu (Jens Dreger)
To: mathgroup at smc.vnet.net
To:	mathgroup at smc.vnet.net

Hi !

Can anyone tell me how I can make MMA take Re[a] for greater than 0 ?


In[1]:= Integrate[E^(-a*x^2), {x, -Infinity, Infinity}]

Out[1]:= If[Re[a] > 0, Sqrt[Pi]/Sqrt[a], 
          Integrate[E^(-a*x^2), {x, -Infinity, Infinity}]]

I would like to have just the answer "Sqrt[Pi]/Sqrt[a]", since I know
that Re[a]>0 is true.

BTW: a/:Re[a]=1 works, but I don't want to specify the real part of a,
just want to say it's greater than zero.

Thanks !

Jens.




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