CHFDV(3)

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

NAME
chfdv - Evaluate a cubic polynomial given in Hermite form and its first derivative at an array of points. While designed for use by PCHFD, 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. If only function values are required, use CHFEV instead.

LIBRARY
SLATEC (PCHIP)

CATEGORY
E3, H1

TYPE
SINGLE PRECISION (CHFDV-S, DCHFDV-D)

KEYWORDS
CUBIC HERMITE DIFFERENTIATION, 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
CHFDV: Cubic Hermite Function and Derivative Evaluator Evaluates the cubic polynomial determined by function values F1,F2 and derivatives D1,D2 on interval (X1,X2), together with its first derivative, at the points XE(J), J=1(1)NE. If only function values are required, use CHFEV, instead. ---------------------------------------------------------------------- Calling sequence: INTEGER NE, NEXT(2), IERR REAL X1, X2, F1, F2, D1, D2, XE(NE), FE(NE), DE(NE) CALL CHFDV (X1,X2, F1,F2, D1,D2, NE, XE, FE, DE, 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 array of points at which the functions are to be evaluated. If any of the XE are outside the interval [X1,X2], a warning error is returned in NEXT. FE -- (output) real array of values of the cubic function defined by X1,X2, F1,F2, D1,D2 at the points XE. DE -- (output) real array of values of the first derivative of the same function 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 . (Output arrays have not been changed in either case.)

REFERENCES
(NONE)

ROUTINES CALLED
XERMSG

REVISION HISTORY (YYMMDD)
811019 DATE WRITTEN
820803 Minor cosmetic changes for release 1.
890411 Added SAVE statements (Vers. 3.2).
890531 Changed all specific intrinsics to generic. (WRB)
890831 Modified array declarations. (WRB)
890831 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)