SUBROUTINE DY (U,IDMN,I,J,UYYY,UYYYY)
C
C THIS PROGRAM COMPUTES SECOND ORDER FINITE DIFFERENCE
C APPROXIMATIONS TO THE THIRD AND FOURTH Y
C PARTIAL DERIVATIVES OF U AT THE (I,J) MESH POINT
C
COMMON /SPLP/ KSWX ,KSWY ,K ,L ,
1 AIT ,BIT ,CIT ,DIT ,
2 MIT ,NIT ,IS ,MS ,
3 JS ,NS ,DLX ,DLY ,
4 TDLX3 ,TDLY3 ,DLX4 ,DLY4
DIMENSION U(IDMN,1)
IF (J.GT.2 .AND. J.LT.(L-1)) GO TO 50
IF (J .EQ. 1) GO TO 10
IF (J .EQ. 2) GO TO 30
IF (J .EQ. L-1) GO TO 60
IF (J .EQ. L) GO TO 80
C
C COMPUTE PARTIAL DERIVATIVE APPROXIMATIONS AT Y=C
C
10 IF (KSWY .EQ. 1) GO TO 20
UYYY = (-5.0*U(I,1)+18.0*U(I,2)-24.0*U(I,3)+14.0*U(I,4)-
1 3.0*U(I,5))/TDLY3
UYYYY = (3.0*U(I,1)-14.0*U(I,2)+26.0*U(I,3)-24.0*U(I,4)+
1 11.0*U(I,5)-2.0*U(I,6))/DLY4
RETURN
C
C PERIODIC AT X=A
C
20 UYYY = (-U(I,L-2)+2.0*U(I,L-1)-2.0*U(I,2)+U(I,3))/TDLY3
UYYYY = (U(I,L-2)-4.0*U(I,L-1)+6.0*U(I,1)-4.0*U(I,2)+U(I,3))/DLY4
RETURN
C
C COMPUTE PARTIAL DERIVATIVE APPROXIMATIONS AT Y=C+DLY
C
30 IF (KSWY .EQ. 1) GO TO 40
UYYY = (-3.0*U(I,1)+10.0*U(I,2)-12.0*U(I,3)+6.0*U(I,4)-U(I,5))/
1 TDLY3
UYYYY = (2.0*U(I,1)-9.0*U(I,2)+16.0*U(I,3)-14.0*U(I,4)+6.0*U(I,5)-
1 U(I,6))/DLY4
RETURN
C
C PERIODIC AT Y=C+DLY
C
40 UYYY = (-U(I,L-1)+2.0*U(I,1)-2.0*U(I,3)+U(I,4))/TDLY3
UYYYY = (U(I,L-1)-4.0*U(I,1)+6.0*U(I,2)-4.0*U(I,3)+U(I,4))/DLY4
RETURN
C
C COMPUTE PARTIAL DERIVATIVE APPROXIMATIONS ON THE INTERIOR
C
50 CONTINUE
UYYY = (-U(I,J-2)+2.0*U(I,J-1)-2.0*U(I,J+1)+U(I,J+2))/TDLY3
UYYYY = (U(I,J-2)-4.0*U(I,J-1)+6.0*U(I,J)-4.0*U(I,J+1)+U(I,J+2))/
1 DLY4
RETURN
C
C COMPUTE PARTIAL DERIVATIVE APPROXIMATIONS AT Y=D-DLY
C
60 IF (KSWY .EQ. 1) GO TO 70
UYYY = (U(I,L-4)-6.0*U(I,L-3)+12.0*U(I,L-2)-10.0*U(I,L-1)+
1 3.0*U(I,L))/TDLY3
UYYYY = (-U(I,L-5)+6.0*U(I,L-4)-14.0*U(I,L-3)+16.0*U(I,L-2)-
1 9.0*U(I,L-1)+2.0*U(I,L))/DLY4
RETURN
C
C PERIODIC AT Y=D-DLY
C
70 CONTINUE
UYYY = (-U(I,L-3)+2.0*U(I,L-2)-2.0*U(I,1)+U(I,2))/TDLY3
UYYYY = (U(I,L-3)-4.0*U(I,L-2)+6.0*U(I,L-1)-4.0*U(I,1)+U(I,2))/
1 DLY4
RETURN
C
C COMPUTE PARTIAL DERIVATIVE APPROXIMATIONS AT Y=D
C
80 UYYY = -(3.0*U(I,L-4)-14.0*U(I,L-3)+24.0*U(I,L-2)-18.0*U(I,L-1)+
1 5.0*U(I,L))/TDLY3
UYYYY = (-2.0*U(I,L-5)+11.0*U(I,L-4)-24.0*U(I,L-3)+26.0*U(I,L-2)-
1 14.0*U(I,L-1)+3.0*U(I,L))/DLY4
RETURN
END
.