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DAE error messages related to NDSolve command

Dear All,

Nice to know you all. I am a new user of Mathematica and just joined this community by today. I hope that I can have discussions with you. Currently I am running a script to obtain some parameters by using FindFit command. While running the script, I got many error messages (please refer to attach.)

So may I know the meaning of each error message? What is DAE? What is the meaning of the DAE solver failed at t=29.01. The solver is intended for index 1 DAE systems and structural analysis indicates that the DAE is structurally singular.

Is that t referring to the t of my simulation? In this case, my simulation time is from t=1 to t=101. If that error message means that there is something wrong at t=29.01, so what went wrong? There are also other error messages such as NDSolve::nderr: Error test failure at t=77.69, unable to continue.

I am not sure what went wrong so I am looking forward to receive your advises. Thanks for your attention and have a nice day.

Best Regards, Intan

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POSTED BY: INTAN SUPRABA
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Dear Sean,

Thanks for your information. Here are some of the error messages:

  • NDSolve::indexss: The DAE solver failed at t = 29.010538367426943`. The solver is intended for index 1 DAE systems and structural analysis indicates that the DAE is structurally singular. >>
  • InterpolatingFunction::dmval: Input value {30.} lies outside the range of data in the interpolating function. Extrapolation will be used. >>
  • General::stop: Further output of InterpolatingFunction::dmval will be suppressed during this calculation. >>
  • General::stop: Further output of InterpolatingFunction::dmval will be suppressed during this calculation. >>
  • General::stop: Further output of NDSolve::nderr will be suppressed during this calculation. >>

I think the error messages are related to the below command: NDSolvecommand

The command is being used to solve the 1st order different equation of those parameters. Parameters s1i, s2i, etc are given as initial parameters. The main purpose of this script is to obtain estimated parameters a11e, a12e, a21e, etc. by using FindFit command. I cant get the end results because I already got those error messages half way.

Here is the same script as attached before to show the initial part of the script to the part when I got the error messages (FindFit script.nb). So far I still cant figure out what went wrong why I got those error messages. So I would like to know how to interpret those error messages to find out which parts are wrong whether it may relate to the input data or to the command itself.

Hence I am looking forward to have further advise from you. Thanks a lot in advance.

Best Regards, Intan

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POSTED BY: INTAN SUPRABA

Hi, If you can include the error messages in your post, this will help us tell you what they mean.

DAE stands for Differential Algebraic Equation. There's more information available about them online. The index of a DAE is how many times the system has to be differentiated to turn into a set of regular differential equations. In this case NDSolve can handle order 1 DAEs.

The notebook attached has many different parts. I would begin by producing the simplest possible example of the problem and removing extraneous material from what is causing the issue. The issue is with NDSolve, so I'd begin by finding what equations were given to NDSolve.

POSTED BY: Sean Clarke
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