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63 lines
2.2 KiB
Fortran
63 lines
2.2 KiB
Fortran
*DECK DPLINT
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SUBROUTINE DPLINT (N, X, Y, C)
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C***BEGIN PROLOGUE DPLINT
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C***PURPOSE Produce the polynomial which interpolates a set of discrete
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C data points.
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C***LIBRARY SLATEC
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C***CATEGORY E1B
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C***TYPE DOUBLE PRECISION (POLINT-S, DPLINT-D)
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C***KEYWORDS POLYNOMIAL INTERPOLATION
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C***AUTHOR Huddleston, R. E., (SNLL)
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C***DESCRIPTION
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C
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C Abstract
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C Subroutine DPLINT is designed to produce the polynomial which
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C interpolates the data (X(I),Y(I)), I=1,...,N. DPLINT sets up
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C information in the array C which can be used by subroutine DPOLVL
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C to evaluate the polynomial and its derivatives and by subroutine
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C DPOLCF to produce the coefficients.
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C
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C Formal Parameters
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C *** All TYPE REAL variables are DOUBLE PRECISION ***
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C N - the number of data points (N .GE. 1)
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C X - the array of abscissas (all of which must be distinct)
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C Y - the array of ordinates
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C C - an array of information used by subroutines
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C ******* Dimensioning Information *******
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C Arrays X,Y, and C must be dimensioned at least N in the calling
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C program.
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C
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C***REFERENCES L. F. Shampine, S. M. Davenport and R. E. Huddleston,
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C Curve fitting by polynomials in one variable, Report
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C SLA-74-0270, Sandia Laboratories, June 1974.
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C***ROUTINES CALLED XERMSG
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C***REVISION HISTORY (YYMMDD)
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C 740601 DATE WRITTEN
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C 891006 Cosmetic changes to prologue. (WRB)
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C 891006 REVISION DATE from Version 3.2
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C 891214 Prologue converted to Version 4.0 format. (BAB)
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C 900315 CALLs to XERROR changed to CALLs to XERMSG. (THJ)
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C 920501 Reformatted the REFERENCES section. (WRB)
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C***END PROLOGUE DPLINT
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INTEGER I,K,KM1,N
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DOUBLE PRECISION DIF,C(*),X(*),Y(*)
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C***FIRST EXECUTABLE STATEMENT DPLINT
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IF (N .LE. 0) GO TO 91
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C(1)=Y(1)
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IF(N .EQ. 1) RETURN
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DO 10010 K=2,N
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C(K)=Y(K)
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KM1=K-1
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DO 10010 I=1,KM1
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C CHECK FOR DISTINCT X VALUES
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DIF = X(I)-X(K)
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IF (DIF .EQ. 0.0) GO TO 92
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C(K) = (C(I)-C(K))/DIF
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10010 CONTINUE
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RETURN
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91 CALL XERMSG ('SLATEC', 'DPLINT', 'N IS ZERO OR NEGATIVE.', 2, 1)
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RETURN
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92 CALL XERMSG ('SLATEC', 'DPLINT',
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+ 'THE ABSCISSAS ARE NOT DISTINCT.', 2, 1)
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RETURN
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END
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