1 REAL*8 AA(513,513), DD(513,513) 2 REAL*8 X (513,513), Y (513,513) 3 REAL*8 RX(513,513), RY(513,513) 4 DO J = 2,N-1 5 DO I = 2,N-1 6 XX = X(I+1,J)-X(I-1,J) 7 YX = Y(I+1,J)-Y(I-1,J) 8 XY = X(I,J+1)-X(I,J-1) 9 YY = Y(I,J+1)-Y(I,J-1) 10 A = 0.25 * (XY*XY+YY*YY) 11 B = 0.25* (XX*XX+YX*YX) 12 C = 0.125 * (XX*XY+YX*YY) 13 AA(I,J) = -B 14 DD(I,J) = B+B+A*REL 15 PXX = X(I+1,J)-2.*X(I,J)+X(I-1,J) 16 QXX = Y(I+1,J)-2.*Y(I,J)+Y(I-1,J) 17 PYY = X(I,J+1)-2.*X(I,J)+X(I,J-1) 18 QYY = Y(I,J+1)-2.*Y(I,J)+Y(I,J-1) 19 PXY = X(I+1,J+1)-X(I+1,J-1)-X(I-1,J+1)+X(I-1,J-1) 20 QXY = Y(I+1,J+1)-Y(I+1,J-1)-Y(I-1,J+1)+Y(I-1,J-1) 21 RX(I,J) = A*PXX+B*PYY-C*PXY 22 RY(I,J) = A*QXX+B*QYY-C*QXY 23 END DO 24 END DO 25