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60 lines
2 KiB
Fortran
60 lines
2 KiB
Fortran
*DECK RPZERO
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SUBROUTINE RPZERO (N, A, R, T, IFLG, S)
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C***BEGIN PROLOGUE RPZERO
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C***PURPOSE Find the zeros of a polynomial with real coefficients.
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C***LIBRARY SLATEC
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C***CATEGORY F1A1A
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C***TYPE SINGLE PRECISION (RPZERO-S, CPZERO-C)
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C***KEYWORDS POLYNOMIAL ROOTS, POLYNOMIAL ZEROS, REAL ROOTS
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C***AUTHOR Kahaner, D. K., (NBS)
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C***DESCRIPTION
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C
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C Find the zeros of the real polynomial
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C P(X)= A(1)*X**N + A(2)*X**(N-1) +...+ A(N+1)
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C
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C Input...
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C N = degree of P(X)
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C A = real vector containing coefficients of P(X),
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C A(I) = coefficient of X**(N+1-I)
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C R = N word complex vector containing initial estimates for zeros
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C if these are known.
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C T = 6(N+1) word array used for temporary storage
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C IFLG = flag to indicate if initial estimates of
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C zeros are input.
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C If IFLG .EQ. 0, no estimates are input.
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C If IFLG .NE. 0, the vector R contains estimates of
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C the zeros
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C ** Warning ****** If estimates are input, they must
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C be separated; that is, distinct or
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C not repeated.
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C S = an N word array
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C
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C Output...
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C R(I) = ith zero,
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C S(I) = bound for R(I) .
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C IFLG = error diagnostic
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C Error Diagnostics...
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C If IFLG .EQ. 0 on return, all is well.
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C If IFLG .EQ. 1 on return, A(1)=0.0 or N=0 on input.
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C If IFLG .EQ. 2 on return, the program failed to converge
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C after 25*N iterations. Best current estimates of the
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C zeros are in R(I). Error bounds are not calculated.
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C
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C***REFERENCES (NONE)
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C***ROUTINES CALLED CPZERO
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C***REVISION HISTORY (YYMMDD)
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C 810223 DATE WRITTEN
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C 890206 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***END PROLOGUE RPZERO
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C
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COMPLEX R(*), T(*)
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REAL A(*), S(*)
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C***FIRST EXECUTABLE STATEMENT RPZERO
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N1=N+1
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DO 1 I=1,N1
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T(I)= CMPLX(A(I),0.0)
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1 CONTINUE
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CALL CPZERO(N,T,R,T(N+2),IFLG,S)
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RETURN
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END
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