Non-autonomous systems

[ivan-pi]

The ROS4 solver of Hairer also supports non-autonomous systems. The interface offers a switch to select between autonomous and non-autonomous:

C     IFCN        GIVES INFORMATION ON FCN:
C                    IFCN=0: F(X,Y) INDEPENDENT OF X (AUTONOMOUS)
C                    IFCN=1: F(X,Y) MAY DEPEND ON X (NON-AUTONOMOUS)

If autonomous, the user provides an extra callback argument:

C     DFX         NAME (EXTERNAL) OF THE SUBROUTINE WHICH COMPUTES
C                 THE PARTIAL DERIVATIVES OF F(X,Y) WITH RESPECT TO X
C                 (THIS ROUTINE IS ONLY CALLED IF IDFX=1 AND IFCN=1;
C                 SUPPLY A DUMMY SUBROUTINE IN THE CASE IDFX=0 OR IFCN=0).
C                 OTHERWISE, THIS SUBROUTINE MUST HAVE THE FORM
C                    SUBROUTINE DFX(N,X,Y,FX)
C                    REAL*8 X,Y(N),FX(N)
C                    FX(1)= ...
C                
C     IDFX        SWITCH FOR THE COMPUTATION OF THE DF/DX:
C                    IDFX=0: DF/DX IS COMPUTED INTERNALLY BY FINITE
C                       DIFFERENCES, SUBROUTINE "DFX" IS NEVER CALLED.
C                    IDFX=1: DF/DX IS SUPPLIED BY SUBROUTINE DFX.