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- *DECK DEI
- DOUBLE PRECISION FUNCTION DEI (X)
- C***BEGIN PROLOGUE DEI
- C***PURPOSE Compute the exponential integral Ei(X).
- C***LIBRARY SLATEC (FNLIB)
- C***CATEGORY C5
- C***TYPE DOUBLE PRECISION (EI-S, DEI-D)
- C***KEYWORDS EI FUNCTION, EXPONENTIAL INTEGRAL, FNLIB,
- C SPECIAL FUNCTIONS
- C***AUTHOR Fullerton, W., (LANL)
- C***DESCRIPTION
- C
- C DEI calculates the double precision exponential integral, Ei(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 Ei(X) = -E1(-X)
- C or
- C E1(X) = -Ei(-X).
- C
- C***REFERENCES (NONE)
- C***ROUTINES CALLED DE1
- C***REVISION HISTORY (YYMMDD)
- C 770701 DATE WRITTEN
- 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***END PROLOGUE DEI
- DOUBLE PRECISION X, DE1
- C***FIRST EXECUTABLE STATEMENT DEI
- DEI = -DE1(-X)
- C
- RETURN
- END
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