SLATEC Routines --- DE1 ---

*DECK DE1
      DOUBLE PRECISION FUNCTION DE1 (X)
C***BEGIN PROLOGUE  DE1
C***PURPOSE  Compute the exponential integral E1(X).
C***LIBRARY   SLATEC (FNLIB)
C***CATEGORY  C5
C***TYPE      DOUBLE PRECISION (E1-S, DE1-D)
C***KEYWORDS  E1 FUNCTION, EXPONENTIAL INTEGRAL, FNLIB,
C             SPECIAL FUNCTIONS
C***AUTHOR  Fullerton, W., (LANL)
C***DESCRIPTION
C
C DE1 calculates the double precision exponential integral, E1(X), for
C positive double precision argument X and the Cauchy principal value
C for negative X.  If principal values are used everywhere, then, for
C all X,
C
C    E1(X) = -Ei(-X)
C or
C    Ei(X) = -E1(-X).
C
C
C Series for AE10       on the interval -3.12500E-02 to  0.
C                                        with weighted error   4.62E-32
C                                         log weighted error  31.34
C                               significant figures required  29.70
C                                    decimal places required  32.18
C
C
C Series for AE11       on the interval -1.25000E-01 to -3.12500E-02
C                                        with weighted error   2.22E-32
C                                         log weighted error  31.65
C                               significant figures required  30.75
C                                    decimal places required  32.54
C
C
C Series for AE12       on the interval -2.50000E-01 to -1.25000E-01
C                                        with weighted error   5.19E-32
C                                         log weighted error  31.28
C                               significant figures required  30.82
C                                    decimal places required  32.09
C
C
C Series for E11        on the interval -4.00000E+00 to -1.00000E+00
C                                        with weighted error   8.49E-34
C                                         log weighted error  33.07
C                               significant figures required  34.13
C                                    decimal places required  33.80
C
C
C Series for E12        on the interval -1.00000E+00 to  1.00000E+00
C                                        with weighted error   8.08E-33
C                                         log weighted error  32.09
C                        approx significant figures required  30.4
C                                    decimal places required  32.79
C
C
C Series for AE13       on the interval  2.50000E-01 to  1.00000E+00
C                                        with weighted error   6.65E-32
C                                         log weighted error  31.18
C                               significant figures required  30.69
C                                    decimal places required  32.03
C
C
C Series for AE14       on the interval  0.          to  2.50000E-01
C                                        with weighted error   5.07E-32
C                                         log weighted error  31.30
C                               significant figures required  30.40
C                                    decimal places required  32.20
C
C***REFERENCES  (NONE)
C***ROUTINES CALLED  D1MACH, DCSEVL, INITDS, XERMSG
C***REVISION HISTORY  (YYMMDD)
C   770701  DATE WRITTEN
C   890531  Changed all specific intrinsics to generic.  (WRB)
C   891115  Modified prologue description.  (WRB)
C   891115  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   920618  Removed space from variable names.  (RWC, WRB)
C***END PROLOGUE  DE1