# SLATEC Routines --- BESYNU ---

```*DECK BESYNU
SUBROUTINE BESYNU (X, FNU, N, Y)
C***BEGIN PROLOGUE  BESYNU
C***SUBSIDIARY
C***PURPOSE  Subsidiary to BESY
C***LIBRARY   SLATEC
C***TYPE      SINGLE PRECISION (BESYNU-S, DBSYNU-D)
C***AUTHOR  Amos, D. E., (SNLA)
C***DESCRIPTION
C
C     Abstract
C         BESYNU computes N member sequences of Y Bessel functions
C         Y/SUB(FNU+I-1)/(X), I=1,N for non-negative orders FNU and
C         positive X. Equations of the references are implemented on
C         small orders DNU for Y/SUB(DNU)/(X) and Y/SUB(DNU+1)/(X).
C         Forward recursion with the three term recursion relation
C         generates higher orders FNU+I-1, I=1,...,N.
C
C         To start the recursion FNU is normalized to the interval
C         -0.5.LE.DNU.LT.0.5. A special form of the power series is
C         implemented on 0.LT.X.LE.X1 while the Miller algorithm for the
C         K Bessel function in terms of the confluent hypergeometric
C         function U(FNU+0.5,2*FNU+1,I*X) is implemented on X1.LT.X.LE.X
C         Here I is the complex number SQRT(-1.).
C         For X.GT.X2, the asymptotic expansion for large X is used.
C         When FNU is a half odd integer, a special formula for
C         DNU=-0.5 and DNU+1.0=0.5 is used to start the recursion.
C
C         BESYNU assumes that a significant digit SINH(X) function is
C         available.
C
C     Description of Arguments
C
C         Input
C           X      - X.GT.0.0E0
C           FNU    - Order of initial Y function, FNU.GE.0.0E0
C           N      - Number of members of the sequence, N.GE.1
C
C         Output
C           Y      - A vector whose first N components contain values
C                    for the sequence Y(I)=Y/SUB(FNU+I-1), I=1,N.
C
C     Error Conditions
C         Improper input arguments - a fatal error
C         Overflow - a fatal error
C
C***REFERENCES  N. M. Temme, On the numerical evaluation of the ordinary
C                 Bessel function of the second kind, Journal of
C                 Computational Physics 21, (1976), pp. 343-350.
C               N. M. Temme, On the numerical evaluation of the modified
C                 Bessel function of the third kind, Journal of
C                 Computational Physics 19, (1975), pp. 324-337.
C***ROUTINES CALLED  GAMMA, R1MACH, XERMSG
C***REVISION HISTORY  (YYMMDD)
C   800501  DATE WRITTEN
C   890531  Changed all specific intrinsics to generic.  (WRB)
C   891214  Prologue converted to Version 4.0 format.  (BAB)
C   900315  CALLs to XERROR changed to CALLs to XERMSG.  (THJ)
C   900326  Removed duplicate information from DESCRIPTION section.
C           (WRB)
C   900328  Added TYPE section.  (WRB)
C   900727  Added EXTERNAL statement.  (WRB)
C   910408  Updated the AUTHOR and REFERENCES sections.  (WRB)
C   920501  Reformatted the REFERENCES section.  (WRB)
C***END PROLOGUE  BESYNU
```