DCHFEV(3)

SYNOPSIS
SUBROUTINE DCHFEV (X1, X2, F1, F2, D1, D2, NE, XE, FE, NEXT, IERR)

NAME
dchfev - Evaluate a cubic polynomial given in Hermite form at an array of points. While designed for use by DPCHFE, it may be useful directly as an evaluator for a piecewise cubic Hermite function in applications, such as graphing, where the interval is known in advance.

LIBRARY
SLATEC (PCHIP)

CATEGORY
E3

TYPE
DOUBLE PRECISION (CHFEV-S, DCHFEV-D)

KEYWORDS
CUBIC HERMITE EVALUATION, CUBIC POLYNOMIAL EVALUATION, PCHIP

AUTHOR
Fritsch, F. N., (LLNL) Lawrence Livermore National Laboratory P.O. Box 808 (L-316) Livermore, CA 94550 FTS 532-4275, (510) 422-4275

DESCRIPTION
DCHFEV: Cubic Hermite Function EValuator Evaluates the cubic polynomial determined by function values F1,F2 and derivatives D1,D2 on interval (X1,X2) at the points XE(J), J=1(1)NE. ---------------------------------------------------------------------- Calling sequence: INTEGER NE, NEXT(2), IERR DOUBLE PRECISION X1, X2, F1, F2, D1, D2, XE(NE), FE(NE) CALL DCHFEV (X1,X2, F1,F2, D1,D2, NE, XE, FE, NEXT, IERR) Parameters: X1,X2 -- (input) endpoints of interval of definition of cubic. (Error return if X1.EQ.X2 .) F1,F2 -- (input) values of function at X1 and X2, respectively. D1,D2 -- (input) values of derivative at X1 and X2, respectively. NE -- (input) number of evaluation points. (Error return if NE.LT.1 .) XE -- (input) real*8 array of points at which the function is to be evaluated. If any of the XE are outside the interval [X1,X2], a warning error is returned in NEXT. FE -- (output) real*8 array of values of the cubic function defined by X1,X2, F1,F2, D1,D2 at the points XE. NEXT -- (output) integer array indicating number of extrapolation points: NEXT(1) = number of evaluation points to left of interval. NEXT(2) = number of evaluation points to right of interval. IERR -- (output) error flag. Normal return: IERR = 0 (no errors). "Recoverable" errors: IERR = -1 if NE.LT.1 . IERR = -2 if X1.EQ.X2 . (The FE-array has not been changed in either case.)

REFERENCES
(NONE)

ROUTINES CALLED
XERMSG

REVISION HISTORY (YYMMDD)
811019 DATE WRITTEN
820803 Minor cosmetic changes for release 1.
870813 Corrected XERROR calls for d.p. names(s).
890206 Corrected XERROR calls.
890411 Added SAVE statements (Vers. 3.2).
890531 Changed all specific intrinsics to generic. (WRB)
890703 Corrected category record. (WRB)
890831 Modified array declarations. (WRB)
891006 Cosmetic changes to prologue. (WRB)
891006 REVISION DATE from Version 3.2
891214 Prologue converted to Version 4.0 format. (BAB)
900315 CALLs to XERROR changed to CALLs to XERMSG. (THJ)