Definition:Cosine Integral Function

Definition
The cosine integral function is the real function $\Ci: \R_{>0} \to \R$ defined as:


 * $\map \Ci x = \ds \int_{t \mathop = x}^{t \mathop \to +\infty} \frac {\cos t} t \rd t$

Graph

 * CiFunction.png

Also defined as
Some sources give this as:


 * $\map \Ci x = \ds -\int_{t \mathop = x}^{t \mathop \to +\infty} \frac {\cos t} t \rd t$

The difference between this and the definition given is trivial, but it is important to check results using this concept to confirm which version is being used.

Also see

 * Characterization of Cosine Integral Function


 * Definition:Sine Integral Function