derkf derkf_int

derkf_int() def derkf_int ( n  , t  , y  , wsave    ) Initial value problem of a system of first order ordinary differential equations (5(4)-th order Runge-Kutta-Fehlberg method) (Interpolation for dense output) Purpose This is the support routine which interpolates the solution for dense output when an initial value problem of a system of ordinary differential equations is solved by derkf. For the details of interpolants used here, refer to the reference below. derkf must be called with setting parameter mode = 2 to enable dense output. Additional function evaluation for dense output is not required. When returned from derkf with info1 = 2 (info1 = 1 for last step) after accepted step, the interpolated solution within latest step interval can be computed by using this routine. Returns info (int) = 0: Successful exit. = -1: The argument n had an illegal value. (n < 1) = -3: The argument y is invalid. = -4: The argument wsave is invalid. Parameters [in] n Number of differential equations. (n >= 1) [in] t t at which the interpolated solution is computed. t must be in the interval of the last step. That is, t1 <= t <= t2 where t1 is the value of t on the previous return from derkf with info1 = 2, and t2 is the value on the last return with info1 = 2. [out] y Numpy ndarray (1-dimensional, float, n) Interpolated solution at t. [out] wsave Numpy ndarray (1-dimensional, float, length 11*n + 20) Data save area used by derkf. Reference W H Enright et al. "Interpolants for Runge-Kutta Formulas" ACM Transactions on Mathematical Software Vol.12, No.3, 1986, pp.193-218 Example Program See example program (2) of derkf.