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meix.f
Go to the documentation of this file.
Or view
the newest version in sPHENIX GitHub for file meix.f
1
C+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
2
C++ Copyright S. Zhang and J. M. Jing ++
3
C++ Computation of Special Functions, John Wiley & Sons, New York, ++
4
C++ 1996 and http://jin.ece.illinois.edu . ++
5
C+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
6
C
7
SUBROUTINE
eix
(X,EI)
8
C
9
C ============================================
10
C Purpose: Compute exponential integral Ei(x)
11
C Input : x --- Argument of Ei(x)
12
C Output: EI --- Ei(x) ( x > 0 )
13
C ============================================
14
C
15
IMPLICIT
DOUBLE PRECISION
(a-
h
,o-
z
)
16
IF
(
x
.EQ.0.0)
THEN
17
ei
=-1.0d+300
18
ELSE
IF
(
x
.LE.40.0)
THEN
19
ei
=1.0d0
20
r
=1.0d0
21
DO
15
k
=1,100
22
r
=
r
*
k
*
x
/(
k
+1.0d0)**2
23
ei
=
ei
+
r
24
IF
(dabs(
r
/
ei
).LE.1.0d-15)
go
to
20
25
15
CONTINUE
26
20 ga=0.5772156649015328d0
27
ei
=ga+dlog(
x
)+
x
*
ei
28
ELSE
29
ei
=1.0d0
30
r
=1.0d0
31
DO
25
k
=1,20
32
r
=
r
*
k
/
x
33
25
ei
=
ei
+
r
34
ei
=dexp(
x
)/
x
*
ei
35
ENDIF
36
RETURN
37
END
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