e1.f
FUNCTION E1 (X)
C***BEGIN PROLOGUE E1
C***PURPOSE Compute the exponential integral E1(X).
C***LIBRARY SLATEC (FNLIB)
C***CATEGORY C5
C***TYPE SINGLE PRECISION (E1-S, DE1-D)
C***KEYWORDS E1 FUNCTION, EXPONENTIAL INTEGRAL, FNLIB,
C SPECIAL FUNCTIONS
C***AUTHOR Fullerton, W., (LANL)
C***DESCRIPTION
C
C E1 calculates the single precision exponential integral, E1(X), for
C positive single 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 AE11 on the interval -1.00000D-01 to 0.
C with weighted error 1.76E-17
C log weighted error 16.75
C significant figures required 15.70
C decimal places required 17.55
C
C
C Series for AE12 on the interval -2.50000D-01 to -1.00000D-01
C with weighted error 5.83E-17
C log weighted error 16.23
C significant figures required 15.76
C decimal places required 16.93
C
C
C Series for E11 on the interval -4.00000D+00 to -1.00000D+00
C with weighted error 1.08E-18
C log weighted error 17.97
C significant figures required 19.02
C decimal places required 18.61
C
C
C Series for E12 on the interval -1.00000D+00 to 1.00000D+00
C with weighted error 3.15E-18
C log weighted error 17.50
C approx significant figures required 15.8
C decimal places required 18.10
C
C
C Series for AE13 on the interval 2.50000D-01 to 1.00000D+00
C with weighted error 2.34E-17
C log weighted error 16.63
C significant figures required 16.14
C decimal places required 17.33
C
C
C Series for AE14 on the interval 0. to 2.50000D-01
C with weighted error 5.41E-17
C log weighted error 16.27
C significant figures required 15.38
C decimal places required 16.97
C
C***REFERENCES (NONE)
C***ROUTINES CALLED CSEVL, INITS, R1MACH, 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 E1