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12-02-2015
06:45 PM

12-02-2015
06:45 PM

Error in Solving an Initial Value Problem

Hi Folks,

I'm getting an error in what should be a very simple ODE solution. The error says that I have too many initial conditions, but a second order problem requires two initial conditions.

I'm probably making some bush league mistake, but I just don't see it.

I would most appreciate any suggestions.

Mark

P.S. I can upload the mcad file if that helps.

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12-02-2015
07:15 PM

12-02-2015
07:15 PM

Re: Error in Solving an Initial Value Problem

1) If you have a question, then create a question here, not a document.

2) If possible, always attach you Mathcad file and state, which version you are using

Mathcad is quite limited when it come to differential equation. In your case it seems, the squaring the second derivative is something which Mathcad does not like.

If you create a workaround using the square root, you get a solution, but not the 1/2*sin(2x) you expected.

Mathcad gives you y=x, which is a solution to your DE as well ;-)

WE

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12-03-2015
01:50 PM

12-03-2015
01:50 PM

Re: Error in Solving an Initial Value Problem

Hi Werner,

Thanks very much for the quick reply. I'm doing the solution in MCAD15. You are correct that y=x is a solution that satisfies the initial conditions. I tried starting the solution at a small, non-zero value of x and using the second derivative as one of the corresponding initial conditions. I had hoped to nudge the solver to the sinusoidal rather than the straight line solution. However, it also gave an error.

I'm not sure how to attach the file to this message. Do I need to start another thread?

Mark

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