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05-29-2013
04:44 PM

05-29-2013
04:44 PM

Hello,

This is my first post. I have been trying to get the ODESOLVER to work in the PRIME 2.0. It took me awhile to get even the help examples to work. I think I figured out that you have to use the ctrl+= when you set the constraints like in MATHCAD 15, but the help files do not tell you that. I figured that out by watching some u-tube videos.

In any case, I am trying to solve a simple ODE to plot the displacement of a particle given a velocity function. The application is applying ocean wave theory.

Any help would be appreciated, I have spent too much time trying to figure out this simple problem so I can then add other velocity compents to get my final answer.

My file is attached.

Thanks.

John T.

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05-29-2013
05:05 PM

05-29-2013
05:05 PM

Basically you had too much initial condition - for a DE of first order you can have only one IC, not two!

Funny that Prime's error message is telling the exact opposite, it say that you have too few ICs.

See attached

5 REPLIES 5

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05-29-2013
05:05 PM

05-29-2013
05:05 PM

Basically you had too much initial condition - for a DE of first order you can have only one IC, not two!

Funny that Prime's error message is telling the exact opposite, it say that you have too few ICs.

See attached

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05-29-2013
05:27 PM

05-29-2013
05:27 PM

Re: Odesolver

Werner,

Thanks so much. Thanks makes total sense and I could not figure out what other equations it wanted.

So to confirm you do have to use the CTR+= in the constraints, it works but just want to make sure....the documentation is poor.

John

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05-29-2013
05:36 PM

05-29-2013
05:36 PM

Re: Odesolver

So to confirm you do have to use the CTR+= in the constraints, it works but just want to make sure....the documentation is poor.

I guess the doc in Mathcad 15 is better, as is the whole program. Unfortunately Prime is the future and as its still unfinished and a work in progress (never understood why they call it version 2.0 instead of 0.2) we can only hope it will get better.

And, yes, you have to use the boolean equal sign for initial conditions and constraints.

Mathcad has a lot of different equal signs, for assignments (:=), numeric evaluation (=), boolean conditions /the "fat" =), symbolic evaluation (-->), local assignments in programs (<--) and in MC15 another one for global assignments. But this makes sense.

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05-30-2013
01:07 PM

05-30-2013
01:07 PM

Re: Odesolver

Thanks Werner.

I am working my way through the problem and adding complexity as I go along for the whole problem. If given an acceleration ODE I would need two boundary conditions to solve for displacement. That is the real problem I am trying to solve and now I get a "units not compatible" error. It looks right to me....any thoughts on why this does not work.

Thanks so much...see attached Prime 2 file.

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05-30-2013
01:42 PM

05-30-2013
01:42 PM

Re: Odesolver

You demand that the second derivative of x(t) should be udot.wave(t). So you cannot have x''(..)=... as an initial condition. The second derivative of x(t) is defined by udot.wave(t). So the condition x(0)=0 is redundant and in effect we would miss an IC, the condition x(1)=5 would be a discrepancy and an error.

Instead you coul demand that x'(0s)=7 ft/sec or anything like that.