# exprel.f

          FUNCTION EXPREL (X)
    C***BEGIN PROLOGUE  EXPREL
    C***PURPOSE  Calculate the relative error exponential (EXP(X)-1)/X.
    C***LIBRARY   SLATEC (FNLIB)
    C***CATEGORY  C4B
    C***TYPE      SINGLE PRECISION (EXPREL-S, DEXPRL-D, CEXPRL-C)
    C***KEYWORDS  ELEMENTARY FUNCTIONS, EXPONENTIAL, FIRST ORDER, FNLIB
    C***AUTHOR  Fullerton, W., (LANL)
    C***DESCRIPTION
    C
    C Evaluate  EXPREL(X) = (EXP(X) - 1.0) / X.   For small ABS(X) the
    C Taylor series is used.  If X is negative, the reflection formula
    C         EXPREL(X) = EXP(X) * EXPREL(ABS(X))
    C may be used.  This reflection formula will be of use when the
    C evaluation for small ABS(X) is done by Chebyshev series rather than
    C Taylor series.  EXPREL and X are single precision.
    C
    C***REFERENCES  (NONE)
    C***ROUTINES CALLED  R1MACH
    C***REVISION HISTORY  (YYMMDD)
    C   770801  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***END PROLOGUE  EXPREL