# besi1.f

          FUNCTION BESI1 (X)
    C***BEGIN PROLOGUE  BESI1
    C***PURPOSE  Compute the modified (hyperbolic) Bessel function of the
    C            first kind of order one.
    C***LIBRARY   SLATEC (FNLIB)
    C***CATEGORY  C10B1
    C***TYPE      SINGLE PRECISION (BESI1-S, DBESI1-D)
    C***KEYWORDS  FIRST KIND, FNLIB, HYPERBOLIC BESSEL FUNCTION,
    C             MODIFIED BESSEL FUNCTION, ORDER ONE, SPECIAL FUNCTIONS
    C***AUTHOR  Fullerton, W., (LANL)
    C***DESCRIPTION
    C
    C BESI1(X) calculates the modified (hyperbolic) Bessel function
    C of the first kind of order one for real argument X.
    C
    C Series for BI1        on the interval  0.          to  9.00000D+00
    C                                        with weighted error   2.40E-17
    C                                         log weighted error  16.62
    C                               significant figures required  16.23
    C                                    decimal places required  17.14
    C
    C***REFERENCES  (NONE)
    C***ROUTINES CALLED  BESI1E, CSEVL, INITS, R1MACH, XERMSG
    C***REVISION HISTORY  (YYMMDD)
    C   770401  DATE WRITTEN
    C   890531  Changed all specific intrinsics to generic.  (WRB)
    C   890531  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   900326  Removed duplicate information from DESCRIPTION section.
    C           (WRB)
    C***END PROLOGUE  BESI1