Avoid long output, Real variables?

*To*: mathgroup at smc.vnet.net*Subject*: [mg20424] Avoid long output, Real variables?*From*: bergervo at prl.philips.nl (Bergervoet J.R.M.)*Date*: Tue, 26 Oct 1999 00:33:08 -0400*Organization*: Philips Research Laboratories Eindhoven, Netherlands*Sender*: owner-wri-mathgroup at wolfram.com

Is it possible to tell Mathematica that a variable, x, is Real? I am looking for commands like those of some competing vendor: assume(x, real) assume(x>0) If I cannot declare x to be Real, I get clumsy answers. For instance, a Fourier transform which for real x is just: 2 BesselK[0, x Sign[x]] gives me instead a pretty long answer where the actual solution for real x is hardly recognizable between the rest: In[4]:=Integrate[E^(I*k*x)/Sqrt[1+k^2]/(2*Pi), {k,-Infinity,Infinity}] Out[4]= If[Im[x] == 0, 2 BesselK[0, x Sign[x]], I k x E Integrate[------------, {k, -Infinity, Infinity}]] / (2 Pi) 2 Sqrt[1 + k ] In[5]:= And it can get worse if several variables are involved. So I really hope that someone can teach me how to declare them Real (or positive). Thanks in advance, Jos