Solve 2 odes - nonlinear

Hi,
I have been trying to solve 2 odes over time in labview but I can't quite get it. I think my problem is that they are non-linear and I am going about it the wrong way. I have been trying to get a result from the Runge Kutta 4th Order.vi but it does not give me an output.
my equations are:
dxi/dt=(Ch*xi*(r - (xi^2 + yi^2)^(1/2)))/((xi^2 + yi^2)^(1/2)*((r - (xi^2 + yi^2)^(1/2))^2 + 1)^(1/2))+(Cr*(xi - xj))/(Lr*exp(((xi - xj)^2 + (yi - yj)^2)^(1/2)/Lr)*((xi - xj)^2 + (yi - yj)^2)^(1/2))
dy/dt=(Ch*yi*(r - (xi^2 + yi^2)^(1/2)))/((xi^2 + yi^2)^(1/2)*((r - (xi^2 + yi^2)^(1/2))^2 + 1)^(1/2))+(Cr*(yi - yj))/(Lr*exp(((xi - xj)^2 + (yi - yj)^2)^(1/2)/Lr)*((xi - xj)^2 + (yi - yj)^2)^(1/2))
I have constants for all parameters except for xi and yi which should change. I know that (xi^2 + yi^2)^(1/2))^2 should be equal to r in the end.
If some one can point me in the corect direction that would be great.
Thanks
Adam

Hi Adam
I will be looking into your ODE issue for you and trying to help you solve the problem and continue with your application. As I understand you are trying to solve 2 ODE's using LabVIEW but are coming across some issues and hence not getting the data you would expect.
There are a few different things that I think you would benefit from looking into, so I have included a few links for you to look at.
1) If you have the code working in Matlab already, have you thought of converting the code into LabVIEW instead of rewriting?
2) There is now a tool available that will convert expressions directly into code, this may help you place the nodes that you need. The videos on this page show the functionality of this tool.
3) In the LabVIEW add-on Control Design and Simulation Module, there is an example that simulates the Lorenz Attractor along with a number of other functions, this add-on may be something to consider.
4) and lastly in LabVIEW itself I found a few examples on ODE, that use differing methods. Looking at these may help discover where the issue is with your code. Examples in LabVIEW can be found by navigating to help>>find examples>>browse>>analyzing and processing signals>>mathematics>>ODE searching ODE in the example pop-up box may also throw up some useful documents.
If you would like to have a look into these and let me know how your application is going that would be great. If you are still having some issues we can go further into the problem, just let me know how it goes.
Thank you
Stephanie L
Applications Engineer
National Instruments UK and Ireland

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Also remember that the argument to trigonometric functions must be in radians here.
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Solved!
Go to Solution.
Attachments:
NI Forums.zip ‏265 KB

Hello Mark,
Thanks for your reply, I was concerned that I had sent up an air ball on this one! And thank you for taking the time to review the code.
You are correct, I am having an issue with the results of the nD Nonlinear System Solver (VI).vi. And that is a good poiint you raise, regarding the choice of the starting points. I'm not intending to use random values, I think I'm using a number very close to the start angle (in this case 20.001 degrees) as a start and 2pi (or 360 degrees) as the end. When I read the description of the start and end from the documentation:
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I have to admit I don't *understand* what this means and I am currently guessing for the choices of start and end. I will think on this some more and review your links.
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Solved!
Go to Solution.
Attachments:
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Solved!
Go to Solution.

Hi,
MathScript does not support inline user-defined function (UDF). What you need to do is
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Solved!
Go to Solution.

Hi Willy,
I am sorry, I can not upload the VI some of the content is confidential. I have attached a larger picture of the section were the change in volume and time is calculated, dV and dt. Also I have marked the two memory functions used. Hopefully this can help.
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06-05-2014 21-20-00.png ‏52 KB

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Solved!
Go to Solution.
Attachments:
Screen Shot 2014-12-02 at 09.58.08.png ‏60 KB

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帖子被myafu在12-22-2006 01:33 AM时编辑过了

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Solve 2 odes - nonlinear

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