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