CTITLESAFF3DG - DETERMINE TRAPEZOIDAL WEIGHTING FACTOR
C***********************************************************************
C                 COPYRIGHT ATLANTIC RICHFIELD COMPANY 1991            *
C***********************************************************************
CABS SAFF3DG - DETERMINE TRAPEZOIDAL WEIGHTING FACTOR
C
CREAL FUNCTION SAFF3DG
C
C     REAL FUNCTION SAFF3DG( W,W1,W2,W3,W4 )
C
C     COPYRIGHT ATLANTIC RICHFIELD COMPANY 1991.
C
C     ALL RIGHTS RESERVED.  NO PART OF THIS PROGRAM MAY BE PHOTOCOPIED,
C     REPRODUCED, OR  TRANSLATED TO ANOTHER PROGRAM LANGUAGE WITHOUT THE
C     PRIOR CONSENT OF ATLANTIC RICHFIELD COMPANY.
C
C
CA    DESIGNER             D CORRIGAN
CA    AUTHOR               D CORRIGAN
CA    LANGUAGE             FORTRAN 77
CA    SYSTEM               IBM/CRAY
CA    WRITTEN              10-03-86
CA
CA    PURPOSE OF PROGRAM:
CA
CA    DETERMINE THE TRAPEZOIDAL WEIGHTING FACTOR APPROPRIATE
CA    FOR W WHEN W1,W2,W3, AND W4 DEFINE A TRAPEZOID
CA
CA           IF W.LT.W1 .OR. W.GT.W4, SAFF3DG = 0
CA
CA           IF W.GT.W2 .AND. W.LT.W3, SAFF3DG = 1.
CA
CA              W.GT.W1 .AND. W.LT.W2
CA           IF         .OR.           LINEARLY INTERPOLATE
CA              W.GT.W3 .AND. W.LT.W4
CA
CA           W1 < W2 < OR = W3 < W4
CA
CA    ARGUMENTS:
CA
CA
CA    W1,W2,W3,W4  INPUT    REAL  THE FOUR POINTS WHICH DEFINE A
CA                                TRAPEZOID.
CA
CA    W            INPUT    REAL  THE POINT FOR WHICH WEIGHTING IS TO BE
CA                                DETERMINED.
CA                                ARRAY BY THE ROUTINE FFT991 WHICH
CA                                PERFORMS THE Z-DOMAIN FFT IN PARALLEL
CA
CA    EJECT
CAEND
C***********************************************************************
C
C     LOCAL VARIABLES
C
C     D   -  EITHER THE DIFFERENCE W-W1 OR W-W2
C     DW  -  EITHER THE DIFFERENCE W2-W1 OR W4-W3
C
C***********************************************************************
C
      REAL FUNCTION SAFF3DG( W,W1,W2,W3,W4 )
C
      IMPLICIT INTEGER (A-Z)
C
      REAL       W,W1,W2,W3,W4,DW,D
C
      SAFF3DG = 0.
      IF (W .LE. W1) RETURN
      IF (W .GE. W4) RETURN
C
      SAFF3DG = 1.
      IF (W .LT. W2) GO TO 100
      IF (W .GT. W3) GO TO 120
C
      RETURN
C
 100  CONTINUE
      DW = W2 - W1
      D = W - W1
      GO TO 140
C
 120  CONTINUE
      DW = W4 - W3
      D = W4 - W
C
 140  CONTINUE
      SAFF3DG = D / DW
C
      RETURN
      END