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# System of 2 second order coupled differential equations with Mathcad

## System of 2 second order coupled differential equations with Mathcad

(OP)
Hello,

Using Mathcad to solve a system of 2 second order coupled differential equations, I issue a problem with the "D" function (used to solve a diffrentiel equation) when there is more than 1 parameter inside.

Here is the system :

I convert this system to have only first order equations :

Then, I can't find other way than making a D matrix with my parameters :

Then, I issue my problem : its seems that mathcad refuse to have a D function with more than 1 parameter :

So, if anybody here can find a way to solve this system, please let me know !

Regards

Kevin

### RE: System of 2 second order coupled differential equations with Mathcad

You need to define your system of equations in a different way. The standard method is to create a single state vector from all of the DEs.

You can also incorporate the parameters A, B and K into the DE, setting their derivatives to be 0.

Read the Help on rkfixed for further information.

### RE: System of 2 second order coupled differential equations with Mathcad

I don't think the D array can be a two dimensional array. Here is an example controlling the level of a second tank of a two tank system
Scroll down to get to the D array. There is a lot of extra stuff.

Peter Nachtwey
Delta Computer Systems
http://www.deltamotion.com

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