CHFEV Subroutine

subroutine CHFEV(X1, X2, F1, F2, D1, D2, NE, XE, FE, NEXT, IERR)

BEGIN PROLOGUE CHFEV PURPOSE Evaluate a cubic polynomial given in Hermite form at an array of points. While designed for use by PCHFE, 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 SINGLE 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

  CHFEV:  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
REAL  X1, X2, F1, F2, D1, D2, XE(NE), FE(NE)

CALL  CHFEV (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 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 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. 890411 Added SAVE statements (Vers. 3.2). 890531 Changed all specific intrinsics to generic. (WRB) 890703 Corrected category record. (WRB) 890703 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) END PROLOGUE CHFEV Programming notes:

To produce a double precision version, simply: a. Change CHFEV to DCHFEV wherever it occurs, b. Change the real declaration to double precision, and c. Change the constant ZERO to double precision.

DECLARE ARGUMENTS.

**FIRST EXECUTABLE STATEMENT CHFEV

Arguments