Re: Help: piecewise functions
- To: mathgroup at smc.vnet.net
- Subject: [mg50133] Re: Help: piecewise functions
- From: Jens-Peer Kuska <kuska at informatik.uni-leipzig.de>
- Date: Tue, 17 Aug 2004 05:00:44 -0400 (EDT)
- Organization: Universitaet Leipzig
- References: <cfi96d$4s5$1@smc.vnet.net>
- Reply-to: kuska at informatik.uni-leipzig.de
- Sender: owner-wri-mathgroup at wolfram.com
Hi,
perhaps D[UnitStep{t],t] is DiracDelta[t] and this is not a
function, it is a distribution and distributions ar only allowed
in integrals ...
Regards
Jens
rik wrote:
>
> hi,
> i'm a italian student and i must integrate and do differentiation of
> piecewise functions like this:
>
> f[t1,t2,t3] ((UnitStep[t3-t1]-UnitStep[t3-4])
> (UnitStep[t2-t1]-UnitStep[t2-5])) + g[t1,t2,t3]
> ((UnitStep[t2]-UnitStep[t2-t1]) (UnitStep[t1-6]-UnitStep[t1-20])) + ...
>
> i would have this:
>
> D[f[t1,t2,t3] ((UnitStep[t3-t1]-UnitStep[t3-4])
> (UnitStep[t2-t1]-UnitStep[t2-5])) +
> g[t1,t2,t3] ((UnitStep[t2]-UnitStep[t2-t1])
> (UnitStep[t1-6]-UnitStep[t1-20])) + ...] "="
> f'[t1,t2,t3] ((UnitStep[t3-t1]-UnitStep[t3-4])
> (UnitStep[t2-t1]-UnitStep[t2-5])) +
> + g'[t1,t2,t3] ((UnitStep[t2]-UnitStep[t2-t1])
> (UnitStep[t1-6]-UnitStep[t1-20])) +
> + D[...]
>
> and this:
>
> Integrate[ f[t1,t2,t3] ((UnitStep[t3-t1]-UnitStep[t3-4])
> (UnitStep[t2-t1]-UnitStep[t2-5])) +
> g[t1,t2,t3] ((UnitStep[t2]-UnitStep[t2-t1])
> (UnitStep[t1-6]-UnitStep[t1-20])) + ...] "="
> Integrate[f[t1,t2,t3]] ((UnitStep[t3-t1]-UnitStep[t3-4])
> (UnitStep[t2-t1]-UnitStep[t2-5])) +
> + Integrate[g[t1,t2,t3]] ((UnitStep[t2]-UnitStep[t2-t1])
> (UnitStep[t1-6]-UnitStep[t1-20])) +
> + Integrate[...]
>
> How i can do? i have seen that the package <<Calculus`Integration` seem do
> the integration of piecewise functions in right way, but i have found
> nothing about differentiation.
>
> Someone can help me?
>
> Thank and S O R R Y for my ridiculous english
>
> Riccardo Piovosi
>
> Florence Italy