### 5.9.7 The cosine integral function:Ci

The Ci command takes as argument a complex number.
Ci returns the value of the cosine integral function Ci at the point, where

Ci(x) =

∫

x
+∞

cos(t)
t

dt = ln(t) + γ +

∫

x
t=0

cos(t) − 1
t

dt

This satisfies Ci(0) = −∞, Ci(−∞) = iπ and Ci(+∞) = 0.
Input:

Ci(1.0)

Output:

0.337403922901

Input:

Ci(-1.0)

Output:

0.337403922901+3.14159265359*i

Input:

Ci(1.0) - Ci(-1.0)

Output:

-3.14159265359*i