4. METHOD OF SOLUTION
Common methods of solution, such as Runge- Kutta and simple extrapolation, often require too small time steps for numerical stability from the fact that big eigenvalues may exist in a system of coupled differential equations. Therefore the back- ward extrapolation technique, also used very effectively in the code COSTANZA, was chosen. GENDY realizes this method for a general system of differential equations, provided that the first partial derivatives can be given.
The program contains a variable time step control which allows short computation times and uniform accuracy. When nonlinearity of the physical system is thought to be important for the accuracy of the solution, an iteration procedure is provided for optional use.