Question for solving ODE using one function.

Hello.

I am trying to solve ODE problems, and have a question.

X = distance

X' = velocity ( X(1) )

X'' = acceleration ( X(2) )

P = pressure ( X(3) ).

function dxdt =  test(t,x)

                                                              % X = distance

dxdt = [    x(2);                                             % X' = Velocity

            -x(2) - (C2 + (x(3) - P2)) * x(1) + (C1 - x(3)) ; % X'' = acceleration 

            1 / x(1)  - 1/x(1) * x(2) ];                     % Here, should be "P"(pressure), but I consider "X(3)" as P. 

                                                             % P' is a function of X, X'.                                                      

                                                             % Is it wrong approach?

P' = 1/x - 1/x*x'

Is there any method for solving X, X', X'', P' together using one function?

A good adviser told me to use "syms". I understood.

But, I want to know another ways, if there are.

[Torsten]

If the three listed equations are correct to get position, velocity and pressure (what I can't tell) - what's the problem ?

[M_king]

Sorry. I was confused about structure, but thanks to you I knew it.

Thank you :)

Answer 1

[Jan]

The standard approach would be:

distance: X(1)
velocity: X(2)
accleration: X(3)
pressure: X(4)

Then you can evaluate the derivatives inside the function to be integrated.

I do not know, what "P2" should be or what your problem is.

[M_king]

Sorry to bother you.

Your answer helped me organize ODE function.

Thanks!