1      SUBROUTINE QUAD(X,Y,XA,YA)
2C
3C***  COMPUTES PARAMETERS FOR QUADRATIC EXTRAPOLATION
4C
5      DIMENSION X(3),Y(3),X2(3)
6      DATA DERIV/4HDERI/
7      DET(A11,A12,A13,A21,A22,A23,A31,A32,A33)= A11*(A22*A33-A23*A32) -
8     1 A21*(A12*A33-A13*A32) + A31*(A12*A23-A13*A22)
9      DO 1000 I=1,3
10 1000 X2(I)=X(I)**2
11      D=DET(X2(1),X(1),1.,X2(2),X(2),1.,X2(3),X(3),1.)
12      A=DET(Y(1),X(1),1.,Y(2),X(2),1.,Y(3),X(3),1.) /D
13      B=DET(X2(1),Y(1),1.,X2(2),Y(2),1.,X2(3),Y(3),1.)/D
14      C=DET(X2(1),X(1),Y(1),X2(2),X(2),Y(2),X2(3),X(3),Y(3))/D
15C
16C     ----TEST FOR TAKING DERIVATIVES
17C
18      IF(YA.EQ.DERIV)GO TO 1010
19C
20      YA=XA*(A*XA+B)+C
21      RETURN
22C
23 1010 YA=2.*A*XA+B
24      RETURN
25      END
26