Re: Re[a]>0 ?

*To*: mathgroup at smc.vnet.net*Subject*: [mg6227] Re: [mg6198] Re[a]>0 ?*From*: "w.meeussen" <w.meeussen at solair4b.eunet.be>*Date*: Fri, 28 Feb 1997 03:21:48 -0500*Sender*: owner-wri-mathgroup at wolfram.com

At 02:53 27-02-97 -0500, Jens Dreger wrote: >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. > > > hi Jens, either after evaluation: In[5]:= Integrate[E^(-a*x^2), {x, -Infinity, Infinity}] Out[5]= If[Re[a] > 0, Sqrt[Pi]/Sqrt[a], Integrate[E^(-a*x^2), {x, -Infinity, Infinity}]] In[6]:= % /. Re[a] > 0 -> True Out[6]= Sqrt[Pi]/Sqrt[a] or better yet, before it: In[30]:= Integrate[E^(-a*x^2), {x, -Infinity, Infinity}, Assumptions -> {Re[a] > 0}] Out[30]= Sqrt[Pi]/Sqrt[a] all the best, Dr. Wouter L. J. MEEUSSEN w.meeussen at solair4b.eunet.be