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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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