How to avoid multiple Jacobian calls

Hi all,

I have a problem: when solving a stiff differential equation system (with analytical jacobian provided by me), I noticed (using the profile viewer) that, over the total 33 hours needed to solve the system, 30 are dedicated to calculate the Jacobian analytical matrix.

Now, the Jacobian matrix is a 11000x11000 matrix and, to be computed it uses a lot of "if" and "for", for this reason it takes so long to be calculated.

The ode23s calls the function 32 times (so every call need approx. 1 hour to compute the Jacobian matrix).

Is it possible to avoid the calculation of the Jacobian matrix at every call? I was wondering if it wasn't possible to calculate it just one time and then exploit other functions or the global variables...

Thanks for your help

[Sina]

For you question you can avoid it one idea is to make Jacobian matrice as global value and if the input is equal to last input avoid solving it and use the previous global value but if input is not the same you must solve it again ....