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Re: ndsolve with discrete, piecewise variable

  • To: mathgroup at
  • Subject: [mg17188] Re: ndsolve with discrete, piecewise variable
  • From: Eckhard Hennig <hennig at>
  • Date: Tue, 20 Apr 1999 01:21:01 -0400
  • Organization: ITWM
  • References: <7fboro$>
  • Sender: owner-wri-mathgroup at

Oscar Stiffelman wrote in message <7fboro$98u at>...

>Can anyone tell me if NDSolve can be used for the following problem?
>I would like to construct a system of differential equations and then use a
>list of data points (piecewise) as the value of one of the variables.
>For example, I might want to build a filter (electrical) where the input
>could be any arbitrary signal, not just a clean mathematical signal.   I
>would like to see the system's response (time-domain value of a specific
>variable) to the input values.
>Is it possible to evaluate this in a discrete manner?  For example, could I
>solve the system using NDSolve and then use the interpolating function in
>the following manner:
>1.  set the "input" variable equal to the first element in the list, and
>the other variables equal to some arbitrary starting condition (i.e. zero)
>2.  evaluate the system using the interpolating function, saving the values
>of every  variable
>3.  set the "input" variable equal to the next element in the list, and set
>the other variables equal to the saved value, and goto 2.
>I would prefer, however, to treat the data points as if they were discrete
>samples of a continuous function, and for Mathematica to generate
>response (also discretely sampled, of course).

Dear Oscar,

take a look at the notebook "Distortion.nb" at

To run the demo you need a copy of our circuit analysis toolbox Analog
Insydes. A time-limited, fully functional evaluation version is available
for download from our web site.

Best regards,


Dipl.-Ing. Eckhard Hennig      mailto:hennig at
Institut fuer Techno- und Wirtschaftsmathematik e.V. (ITWM)
Erwin-Schroedinger-Strasse,  67663 Kaiserslautern,  Germany
  Voice: +49-(0)631-205-3126    Fax: +49-(0)631-205-4139

     ITWM - Makers of Analog Insydes for Mathematica

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