de1.f
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