define a jacobian matrix in odeset for ode15s

Hi guys,

I am using ode15s to solve my ODEs.

It is said that in odeset ( https://au.mathworks.com/help/matlab/ref/odeset.html#f92-1023074), providing information about the Jacobian matrix is critical for reliability and efficiency.

However, now what I have at hand is the mathematical model , where M is the mass matrix. I do not know what kind of jacobian matrix is in my model.

Can anyone offer me how to define a suitable jacobian matrix that can be applied in the odeset for computational reliability and efficiency ?

Many thanks!