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04-17-2017
03:39 PM

04-17-2017
03:39 PM

Problem with ODEsolve

Hello everyone!

I have a question, how can I solve a system of equation, which is consists of three equation (two of them are Differential and other one is not) using ODEsolve or there is some other way?

So I had a system of two differential equation and everything worked just fine, but then I need to add one more equation and this equation is not differential. So I don't know are the ODESOLVE able to solve this kind of systems or not. It keeps telling me, that I have too few initial conditions. File 9 is a file where only 2 equation are solved.

Thanks for your help

18 REPLIES 18

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04-18-2017
09:12 AM

04-18-2017
09:12 AM

Re: Problem with ODEsolve

Hi Vladimir Novikov,

first of all you should do the following changes:

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04-18-2017
09:27 AM

04-18-2017
09:27 AM

Re: Problem with ODEsolve

.) The whole sheet is unitlesse - otherwise I guess we would experience severe problems with odesolve in Mathcad 15 (thats better in Prime). So Vladimir decided to write the supposed units next to the values in a textbox or separate math region for documentation and reference purpose only. This has no effext on the calculations.

I guess Valery would define every unit as being :=1 and then attached them in the unit field.

.) the equations with the "j" also are for refernce purpose only and have no effect on the calculations.

At the moment I haven't digged far enough in the calculations to be able to provide a solution but I guess the problem is, as Vladimir already guessed, that one of the equations is not an ODE.

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04-18-2017
09:35 AM

04-18-2017
09:35 AM

Re: Problem with ODEsolve

I was attaching:

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04-18-2017
09:36 AM

04-18-2017
09:36 AM

Re: Problem with ODEsolve

The things you referred to is not involved in calculation process. Yes, I made my units as a separate text boxes, which is guarantee, that it not going to mess up calculation. Also you said that j is undefined, that's true. But in the equation block there is no calculation at all, so j is not involved in calculation, but in given-odesolve block I change j (mass flow) with Maxwell equation for mass flow.

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04-18-2017
09:39 AM

04-18-2017
09:39 AM

Re: Problem with ODEsolve

Thank you for making my units look not only good and proper but translated from Russian language))) but it is not the case of my problem. My problem is related to finding solution for system of three equation (2 of them is ODE and one is not). I'm looking for a way to solve this system and seems that odesolve is not working properly for this problem.

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04-18-2017
09:41 AM

04-18-2017
09:41 AM

Re: Problem with ODEsolve

I would say that not all the units are written in text boxes, on the contrary, many are written as if they were variables. The first (° C) for sure.

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04-18-2017
09:43 AM

04-18-2017
09:43 AM

Re: Problem with ODEsolve

it is not affecting calculation at all, units are not the reason of problem 100%

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04-18-2017
09:50 AM

04-18-2017
09:50 AM

Re: Problem with ODEsolve

yes you right. all the units and equation with j it's just cosmetic things for report, real calculation begin after given and in given find block everything seems to be defined properly.

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04-18-2017
10:30 AM

04-18-2017
10:30 AM

Re: Problem with ODEsolve

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