How to solve a system of equations mixing non-linear ODE and non-linear "simple" equations?

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NECK
NECK on 10 Apr 2021
Commented: NECK on 14 Apr 2021
I have a system that I want to solve numerically (attached an overview of the form, X1, X2, etc. are the variable, while C1, c2, etc. are constants). I know a bit about how to solve ode with ode45; I also have some ideas about solving common "simple" equations. But in this system, that describes a dynamic of a process, not all equations are ODE; so, I have some challenges with the structure/syntax of ode45. Please, would you shar with me some ideas about how to solve this kind of system with Matlab or simulink?
Thank you.

Answers (1)

Ayham Aljawabrah
Ayham Aljawabrah on 10 Apr 2021
Edited: Ayham Aljawabrah on 10 Apr 2021
The solvers usually able to solve index-1 DAE, not all the equations are apperent but you have too many variables you mostly need to reduce the order of your differential algebraic equation (DAE) system.
The below link shows how to symbolic math toolbox to prepare a DAE system to be solved with Matlab ode solver ode15i, ode15s, ode23s can handle DAE, the link below utilize ode15i
https://www.mathworks.com/help/symbolic/solve-differential-algebraic-equations.html
For more info about DAE, check the below link https://www.mathworks.com/help/matlab/math/solve-differential-algebraic-equations-daes.html
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