Definition:Exponential Integral Function/Formulation 2

Definition

The exponential integral function is the real function $\Ei: \R_{>0} \to \R$ defined as:

$\map \Ei x = \PV_{t \mathop \to -\infty}^{t \mathop = x} \frac {e^t} t \rd t$

where $\PV$ denotes the Cauchy principal value.

Also see

• Results about the exponential integral function can be found here.

Sources

• 1964: Milton Abramowitz and Irene A. Stegun: Handbook of Mathematical Functions ... (next): Introduction: $3$. Auxiliary Functions and Arguments