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decuslib20-02
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decus/20-0026/cnps.doc
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SUBROUTINE CNPS
PURPOSE
COMPUTES THE VALUE OF AN N-TERM EXPANSION IN CHEBYSHEV
POLYNOMIALS WITH COEFFICIENT VECTOR C FOR ARGUMENT VALUE X.
USAGE
CALL CNPS(Y,X,C,N)
DESCRIPTION OF PARAMETERS
Y - RESULT VALUE
X - ARGUMENT VALUE
C - COEFFICIENT VECTOR OF GIVEN EXPANSION
COEFFICIENTS ARE ORDERED FROM LOW TO HIGH
N - DIMENSION OF COEFFICIENT VECTOR C
REMARKS
OPERATION IS BYPASSED IN CASE N LESS THAN 1
SUBROUTINES AND FUNCTION SUBPROGRAMS REQUIRED
NONE
METHOD
DEFINITION
Y=SUM(C(I)*T(I-1,X), SUMMED OVER I FROM 1 TO N).
EVALUATION IS DONE BY MEANS OF BACKWARD RECURSION
USING THE RECURRENCE EQUATION FOR CHEBYSHEV POLYNOMIALS
T(N+1,X)=2*X*T(N,X)-T(N-1,X).