Solve simultaneously 2 ODE & one Non linear algebraic equation. And all are dependent to each other. Is it possible to solve them in a single Function file in MATLAB ?

Example : dy/dt=z*x-2*y^2; dx/dt=x*z^2-sinh(y); z=x^2*y*asinh(z);

I need to solve it simultaneously and need plots between y vs. t & x vs.t & z vs.t

[Daniel Jovin]

Pujari, did you ever manage to solve this system? I am trying to solve a similar system myself.

Answer 1

[Torsten]

Take a look at the section "Solve Robertson Problem As Semi-Explicit Differential Algebraic Equations (DAEs)" under

https://www.mathworks.com/help/matlab/ref/ode15s.html

Best wishes

Torsten.

[PUJARI MURAGA]

Thank you. But any other alternative solution available ?

[Torsten]

Why ? The example exactly does what you are searching for: it handles two differential equations and one algebraic equation simultaneously.

Best wishes

Torsten.

[PUJARI MURAGA]

But actually this is not my original differential equations. My model equations containing 5 ODE & 2 Algebraic equations & that too 3 equations with if conditions. I was able to solve it using simulink but I need to do it in M-file also. How to do it now ? Is it still possible as you suggested ?

[Torsten]

Suitable solvers in MATLAB for DAE-systems are ode15s or ode15i. Usually, it is very important that your initial conditions for the solution variables are consistent, i.e. that the algebraic equations are satisfied when the initial values are inserted.

This is the only advice I can give because I don't know your specific DAE-system.

Best wishes

Torsten.

[PUJARI MURAGA]

Okay.