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- *DECK DBESKS
- SUBROUTINE DBESKS (XNU, X, NIN, BK)
- C***BEGIN PROLOGUE DBESKS
- C***PURPOSE Compute a sequence of modified Bessel functions of the
- C third kind of fractional order.
- C***LIBRARY SLATEC (FNLIB)
- C***CATEGORY C10B3
- C***TYPE DOUBLE PRECISION (BESKS-S, DBESKS-D)
- C***KEYWORDS FNLIB, FRACTIONAL ORDER, MODIFIED BESSEL FUNCTION,
- C SEQUENCE OF BESSEL FUNCTIONS, SPECIAL FUNCTIONS,
- C THIRD KIND
- C***AUTHOR Fullerton, W., (LANL)
- C***DESCRIPTION
- C
- C DBESKS computes a sequence of modified Bessel functions of the third
- C kind of order XNU + I at X, where X .GT. 0, XNU lies in (-1,1),
- C and I = 0, 1, ... , NIN - 1, if NIN is positive and I = 0, 1, ... ,
- C NIN + 1, if NIN is negative. On return, the vector BK(.) contains
- C the results at X for order starting at XNU. XNU, X, and BK are
- C double precision. NIN is an integer.
- C
- C***REFERENCES (NONE)
- C***ROUTINES CALLED D1MACH, DBSKES, XERMSG
- C***REVISION HISTORY (YYMMDD)
- C 770601 DATE WRITTEN
- C 890531 Changed all specific intrinsics to generic. (WRB)
- C 890831 Modified array declarations. (WRB)
- C 890831 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***END PROLOGUE DBESKS
- DOUBLE PRECISION XNU, X, BK(*), EXPXI, XMAX, D1MACH
- SAVE XMAX
- DATA XMAX / 0.D0 /
- C***FIRST EXECUTABLE STATEMENT DBESKS
- IF (XMAX.EQ.0.D0) XMAX = -LOG (D1MACH(1))
- C
- IF (X .GT. XMAX) CALL XERMSG ('SLATEC', 'DBESKS',
- + 'X SO BIG BESSEL K UNDERFLOWS', 1, 2)
- C
- CALL DBSKES (XNU, X, NIN, BK)
- C
- EXPXI = EXP (-X)
- N = ABS (NIN)
- DO 20 I=1,N
- BK(I) = EXPXI * BK(I)
- 20 CONTINUE
- C
- RETURN
- END
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