Environmental Engineering Reference
In-Depth Information
D.4 EXPONENTIAL INTEGRAL
e
−
t
e
t
dt
t
∞
x
∫
∫
0
(D.22)
Ei x
( )
= −
dt
=
,
x
>
t
−
x
−∞
The standard definition of the exponential integral is
is also called an exponential integral. note that
Ei
(
x
) is
related to
E
1
(
x
) by analytic continuation, where
−
xt
e
t
∞
∫
1
0 1
…
(D.21)
E x
( )
=
dt
,
x
>
0
,
n
=
,
,
n
n
Ei
(
−
x
)
= −
E x
( )
(D.23)
1
The function defined by the principal value of the
integral
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