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.