Hello,
I am solving two coupled ODEs, one with respect to time, another to z. An element in the solution of the first ODE is used in the second one. So I have to use the lower-level apply-step function:
(apply-step stepper time y step-size yerr dydt-in dydt-out)
The gsl manual says dydt-in can be a null pointer. I wonder how to use null pointer in apply-step? Thank you.
Leo