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