       Re: DSolve with DiracDelta correction

• To: mathgroup at smc.vnet.net
• Subject: [mg75805] Re: DSolve with DiracDelta correction
• From: dimitris <dimmechan at yahoo.com>
• Date: Fri, 11 May 2007 05:21:39 -0400 (EDT)
• References: <f1unqt\$7si\$1@smc.vnet.net>

```Ooops!

Mathematica 5.2 gives the solution with 6.

Dimitris

=CF/=C7 Steffen Paul =DD=E3=F1=E1=F8=E5:
> Hi
> I tried to solve
> DSolve[{y'[t] + \[Alpha] y[t] == DiracDelta[t], y == 0}, y, t]
>
> and got
>
> -\[ExponentialE]^(-t \[Alpha]) (1 - HeavisideTheta[t])
>
> which is zero for t >0.
>
> The solution is correct but I expected somthing else:
>
> exp( - alpha t) UnitStep(t)
>
> which is zero for t <0 and which is also a solution.
>
> In engineering, these solutions are called impulse responses.
>
> The last solution is physically more usefull , because the system responds
> after the excitation (DiracDelta).
>
>
>
> How can I force Mathematica to give only solutions with nonzero values for t
>  >0 ?
>
>
>
> Regards,
>
> Steffen

```

• Prev by Date: Manipulate[] InputField[]
• Next by Date: v. 6, third argument to rectangle
• Previous by thread: Manipulate[] InputField[]
• Next by thread: v. 6, third argument to rectangle