*DECK PVALUE
SUBROUTINE PVALUE (L, NDER, X, YFIT, YP, A)
C***BEGIN PROLOGUE PVALUE
C***PURPOSE Use the coefficients generated by POLFIT to evaluate the
C polynomial fit of degree L, along with the first NDER of
C its derivatives, at a specified point.
C***LIBRARY SLATEC
C***CATEGORY K6
C***TYPE SINGLE PRECISION (PVALUE-S, DP1VLU-D)
C***KEYWORDS CURVE FITTING, LEAST SQUARES, POLYNOMIAL APPROXIMATION
C***AUTHOR Shampine, L. F., (SNLA)
C Davenport, S. M., (SNLA)
C***DESCRIPTION
C
C Written by L. F. Shampine and S. M. Davenport.
C
C Abstract
C
C The subroutine PVALUE uses the coefficients generated by POLFIT
C to evaluate the polynomial fit of degree L , along with the first
C NDER of its derivatives, at a specified point. Computationally
C stable recurrence relations are used to perform this task.
C
C The parameters for PVALUE are
C
C Input --
C L - the degree of polynomial to be evaluated. L may be
C any non-negative integer which is less than or equal
C to NDEG , the highest degree polynomial provided
C by POLFIT .
C NDER - the number of derivatives to be evaluated. NDER
C may be 0 or any positive value. If NDER is less
C than 0, it will be treated as 0.
C X - the argument at which the polynomial and its
C derivatives are to be evaluated.
C A - work and output array containing values from last
C call to POLFIT .
C
C Output --
C YFIT - value of the fitting polynomial of degree L at X
C YP - array containing the first through NDER derivatives
C of the polynomial of degree L . YP must be
C dimensioned at least NDER in the calling program.
C
C***REFERENCES L. F. Shampine, S. M. Davenport and R. E. Huddleston,
C Curve fitting by polynomials in one variable, Report
C SLA-74-0270, Sandia Laboratories, June 1974.
C***ROUTINES CALLED XERMSG
C***REVISION HISTORY (YYMMDD)
C 740601 DATE WRITTEN
C 890531 Changed all specific intrinsics to generic. (WRB)
C 890531 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 900510 Convert XERRWV calls to XERMSG calls. (RWC)
C 920501 Reformatted the REFERENCES section. (WRB)
C***END PROLOGUE PVALUE
DIMENSION YP(*),A(*)
CHARACTER*8 XERN1, XERN2
C***FIRST EXECUTABLE STATEMENT PVALUE
IF (L .LT. 0) GO TO 12
NDO = MAX(NDER,0)
NDO = MIN(NDO,L)
MAXORD = A(1) + 0.5
K1 = MAXORD + 1
K2 = K1 + MAXORD
K3 = K2 + MAXORD + 2
NORD = A(K3) + 0.5
IF (L .GT. NORD) GO TO 11
K4 = K3 + L + 1
IF (NDER .LT. 1) GO TO 2
DO 1 I = 1,NDER
1 YP(I) = 0.0
2 IF (L .GE. 2) GO TO 4
IF (L .EQ. 1) GO TO 3
C
C L IS 0
C
VAL = A(K2+1)
GO TO 10
C
C L IS 1
C
3 CC = A(K2+2)
VAL = A(K2+1) + (X-A(2))*CC
IF (NDER .GE. 1) YP(1) = CC
GO TO 10
C
C L IS GREATER THAN 1
C
4 NDP1 = NDO + 1
K3P1 = K3 + 1
K4P1 = K4 + 1
LP1 = L + 1
LM1 = L - 1
ILO = K3 + 3
IUP = K4 + NDP1
DO 5 I = ILO,IUP
5 A(I) = 0.0
DIF = X - A(LP1)
KC = K2 + LP1
A(K4P1) = A(KC)
A(K3P1) = A(KC-1) + DIF*A(K4P1)
A(K3+2) = A(K4P1)
C
C EVALUATE RECURRENCE RELATIONS FOR FUNCTION VALUE AND DERIVATIVES
C
DO 9 I = 1,LM1
IN = L - I
INP1 = IN + 1
K1I = K1 + INP1
IC = K2 + IN
DIF = X - A(INP1)
VAL = A(IC) + DIF*A(K3P1) - A(K1I)*A(K4P1)
IF (NDO .LE. 0) GO TO 8
DO 6 N = 1,NDO
K3PN = K3P1 + N
K4PN = K4P1 + N
6 YP(N) = DIF*A(K3PN) + N*A(K3PN-1) - A(K1I)*A(K4PN)
C
C SAVE VALUES NEEDED FOR NEXT EVALUATION OF RECURRENCE RELATIONS
C
DO 7 N = 1,NDO
K3PN = K3P1 + N
K4PN = K4P1 + N
A(K4PN) = A(K3PN)
7 A(K3PN) = YP(N)
8 A(K4P1) = A(K3P1)
9 A(K3P1) = VAL
C
C NORMAL RETURN OR ABORT DUE TO ERROR
C
10 YFIT = VAL
RETURN
C
11 WRITE (XERN1, '(I8)') L
WRITE (XERN2, '(I8)') NORD
CALL XERMSG ('SLATEC', 'PVALUE',
* 'THE ORDER OF POLYNOMIAL EVALUATION, L = ' // XERN1 //
* ' REQUESTED EXCEEDS THE HIGHEST ORDER FIT, NORD = ' // XERN2 //
* ', COMPUTED BY POLFIT -- EXECUTION TERMINATED.', 8, 2)
RETURN
C
12 CALL XERMSG ('SLATEC', 'PVALUE',
+ 'INVALID INPUT PARAMETER. ORDER OF POLYNOMIAL EVALUATION ' //
+ 'REQUESTED IS NEGATIVE -- EXECUTION TERMINATED.', 2, 2)
RETURN
END