       Re: question (for Mathematica 6!)

• To: mathgroup at smc.vnet.net
• Subject: [mg75581] Re: question (for Mathematica 6!)
• From: dimitris <dimmechan at yahoo.com>
• Date: Sat, 5 May 2007 06:12:11 -0400 (EDT)
• References: <f1ept5\$4n1\$1@smc.vnet.net>

```Yes I know these.

I just wonder why until now (5.2) we had for example

Integrate[DiracDelta[x], x]
D[%, x]

UnitStep[x]
DiracDelta[x]

and now this has changed.

Anyway...thanks for you response.

Dimitris

"Owen, HL (Hywel)" <h.l.owen at dl.ac.uk> wrote:

HeavisideTheta is undefined
UnitStep gives 1

Their integrals are the same (for example from -1 to 1).

And:
D[HeavisideTheta[x], x] is DiracDelta[x]
Whereas
D[UnitStep[x], x] is (-1 - DiscreteDelta[x] + UnitStep[-x] +
UnitStep[x])/(1 -
DiscreteDelta[x])

Hywel
=CF/=C7 dimitris =DD=E3=F1=E1=F8=E5:
> I don't have a copy of Mathematica 6 but having spent much time
> reading the online documentation (not only because of curiosity!) I
> have one question...
>
> Can somebody explain me the introduction of the HeavisideTheta
> function
>
> http://reference.wolfram.com/mathematica/ref/HeavisideTheta.html
>
> in version 6?
>
> Note that the UnitStep function is still here
>
> http://reference.wolfram.com/mathematica/ref/UnitStep.html
>
> Dimitris

```

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