Re: Integrating UnitSteps
- To: mathgroup at smc.vnet.net
- Subject: [mg48801] Re: Integrating UnitSteps
- From: Paul Abbott <paul at physics.uwa.edu.au>
- Date: Wed, 16 Jun 2004 07:49:05 -0400 (EDT)
- References: <cap3m9$cab$1@smc.vnet.net> <paul-517690.18014516062004@news.uwa.edu.au> <20040616100735.GA6864@matilda.phys.uu.nl>
- Sender: owner-wri-mathgroup at wolfram.com
Hi Bas: >You wrote: > >> > In[2]:= Integrate[UnitStep[x - 1]/x^2, {x, b, Infinity}] >> > >> > UnitStep[-1 + x] >> > Out[2]= If[b < 1, 1, Integrate[----------------, {x, b, Infinity}]] >> > 2 >> > x >> > >> > Which is correct, in principle. However, I'm trying to get an >> > explicit expression for b>1: >> >> Then you can pass this assumption to the Mathematica integrator: >> > > Assuming[b > 1, Integrate[UnitStep[x - 1]/x^2, {x, b, Infinity}]] > >Unfortunately, that doesn't work: > >In[1]:= Assuming[b > 1, Integrate[UnitStep[x - 1]/x^2, {x, b, Infinity}]] > >Out[1]= Assuming[b > 1, If[b < 1, 1, > > UnitStep[-1 + x] >> Integrate[----------------, {x, b, Infinity}]]] > 2 > x It works for me: In[1]:= $Version Out[1]= "5.0 for Mac OS X (June 10, 2003)" In[2]:= Assuming[b > 1, Integrate[UnitStep[x - 1]/x^2, {x, b, Infinity}]] Out[2]= 1/b Cheers, Paul