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Re: Delay Differential Equations

Yun Zhao wrote:

> Hi,


> Does anyone have experience working with delay differential equations in

> Mathematica 7? I found some help files on wolfram and Mathematica help, but

> the information available there were very limited. If anyone can refer me to

> other online or textual sources, I would really appreciate it. Thank you

> very much.


> Mike




you do not need a delayed differential equation. You simple have a rate 

change somewhere in time and NDSolve can handle this nicely:

sol = p /.

    NDSolve[ {p'[t] == - 0.0123 p[t] - 0.0367  If[t < 37, 0, p[t]],

       p[0] == 30000}

      , p, {t, 0, 120}][[1]];

Plot[sol[t], {t, 0, 120}]

cheers, Daniel Huber

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