SLATEC Routines --- CHFEV ---

*DECK CHFEV
      SUBROUTINE CHFEV (X1, X2, F1, F2, D1, D2, NE, XE, FE, NEXT, IERR)
C***BEGIN PROLOGUE  CHFEV
C***PURPOSE  Evaluate a cubic polynomial given in Hermite form at an
C            array of points.  While designed for use by PCHFE, it may
C            be useful directly as an evaluator for a piecewise cubic
C            Hermite function in applications, such as graphing, where
C            the interval is known in advance.
C***LIBRARY   SLATEC (PCHIP)
C***CATEGORY  E3
C***TYPE      SINGLE PRECISION (CHFEV-S, DCHFEV-D)
C***KEYWORDS  CUBIC HERMITE EVALUATION, CUBIC POLYNOMIAL EVALUATION,
C             PCHIP
C***AUTHOR  Fritsch, F. N., (LLNL)
C             Lawrence Livermore National Laboratory
C             P.O. Box 808  (L-316)
C             Livermore, CA  94550
C             FTS 532-4275, (510) 422-4275
C***DESCRIPTION
C
C          CHFEV:  Cubic Hermite Function EValuator
C
C     Evaluates the cubic polynomial determined by function values
C     F1,F2 and derivatives D1,D2 on interval (X1,X2) at the points
C     XE(J), J=1(1)NE.
C
C ----------------------------------------------------------------------
C
C  Calling sequence:
C
C        INTEGER  NE, NEXT(2), IERR
C        REAL  X1, X2, F1, F2, D1, D2, XE(NE), FE(NE)
C
C        CALL  CHFEV (X1,X2, F1,F2, D1,D2, NE, XE, FE, NEXT, IERR)
C
C   Parameters:
C
C     X1,X2 -- (input) endpoints of interval of definition of cubic.
C           (Error return if  X1.EQ.X2 .)
C
C     F1,F2 -- (input) values of function at X1 and X2, respectively.
C
C     D1,D2 -- (input) values of derivative at X1 and X2, respectively.
C
C     NE -- (input) number of evaluation points.  (Error return if
C           NE.LT.1 .)
C
C     XE -- (input) real array of points at which the function is to be
C           evaluated.  If any of the XE are outside the interval
C           [X1,X2], a warning error is returned in NEXT.
C
C     FE -- (output) real array of values of the cubic function defined
C           by  X1,X2, F1,F2, D1,D2  at the points  XE.
C
C     NEXT -- (output) integer array indicating number of extrapolation
C           points:
C            NEXT(1) = number of evaluation points to left of interval.
C            NEXT(2) = number of evaluation points to right of interval.
C
C     IERR -- (output) error flag.
C           Normal return:
C              IERR = 0  (no errors).
C           "Recoverable" errors:
C              IERR = -1  if NE.LT.1 .
C              IERR = -2  if X1.EQ.X2 .
C                (The FE-array has not been changed in either case.)
C
C***REFERENCES  (NONE)
C***ROUTINES CALLED  XERMSG
C***REVISION HISTORY  (YYMMDD)
C   811019  DATE WRITTEN
C   820803  Minor cosmetic changes for release 1.
C   890411  Added SAVE statements (Vers. 3.2).
C   890531  Changed all specific intrinsics to generic.  (WRB)
C   890703  Corrected category record.  (WRB)
C   890703  REVISION DATE from Version 3.2
C   891214  Prologue converted to Version 4.0 format.  (BAB)
C   900315  CALLs to XERROR changed to CALLs to XERMSG.  (THJ)
C***END PROLOGUE  CHFEV