Hi,

I have been using the Rosenbrocks method for solving a set
of stiff ODE's with algebraic constraints. As I do not obtain a satisfactory solution, I would like to know what is going wrong.
I have checked the Jacobian many times, but do not find any
errors. One point that I am unsure about is the vector yscal
that must be provided as the input. Here I set yscal = max(C,|y|),
where C is a vector with all elements equal to one, as suggested
in numerical recipes. I can mention that I have not rescaled my
variables to nondimensional units, but use the original ones.

Do you have any suggestions of how I can solve this problem?

Thank you in advance

Hi,

Try setting a value of C for each variable that is the approximate size of that variable. If you have variables that start at one size and then get very small, set C to the initial value. Then when the variable decays away, it won't be accurate, but you won't care what its value is.

Hi Kibitzer!

Thank you for your reply. I will definitely try your suggestion.