System of 2 second order coupled differential equations with Mathcad

Then, I issue my problem : its seems that I can't put a D function with 2 parameters in rkfixed method.

Your D function has three parameters, not two. The variable t does not even appear on he RHS, so get rid if it. If that doesn't fix it, please post a worksheet. It's hard to debug a picture.

Kevin Lem wrote: Hello, My problem deals with a system of 2 second order coupled differential equations, Using Mathcad. I issue a problem with the "D" function (used to solve a differential equation) when there is more than 1 parameter inside. Here is the system with 2 parameters Teta1 and Teta2 : I convert this system to have only first order equations : Then, I can't find other way than making a D matrix with my 2 parameters Teta1 and Teta2 Then, I issue my problem : its seems that I can't put a D function with 2 parameters in rkfixed method. So, if anybody here can find a way to solve this system, please let me know ! Any other method to solve it is welcome, of course ! Regards Kevin

Did you look at the answers to this question posed on Eng Tips?

System of 2 second order coupled differential equations with Mathcad - PTC: Mathcad - Eng-Tips

The Mathcad 14/15 ODE solvers do not accept a 2D matrix form for the differential equation.  Instead you must recast it as combined vector.

Stuart