MathGroup Archive: March 2004 [00536]

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Re: Constant function Integrate Assumption

To: mathgroup at smc.vnet.net
Subject: [mg47222] Re: Constant function Integrate Assumption
From: astanoff_otez_ceci at yahoo.fr (astanoff)
Date: Wed, 31 Mar 2004 02:57:57 -0500 (EST)
References: <c4bdnf$6tr$1@smc.vnet.net>
Sender: owner-wri-mathgroup at wolfram.com

Daryl Reece wrote:

> I am trying to use units within an Integration and would like
> Mathematica to understand that the units (Month) are not a function of
> the integration variable, but I have not had any luck with my
> attempts.

> Specifically

> Integrate[UnitStep[t Months], t]

> should yield

> t UnitStep[t]

my solution : 

In[1]:=Unprotect[UnitStep];
UnitStep[t_*unit_ /; MemberQ[Attributes[unit],Constant]]:=UnitStep[t];
Protect[UnitStep];

In[2]:=SetAttributes[Months,Constant];

In[3]:=Integrate[UnitStep[t  Months],t]
Out[3]=t UnitStep[t]

hth
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