Category:Exponential Integral Function

This category contains results about Exponential Integral Function.
Definitions specific to this category can be found in Definitions/Exponential Integral Function.

Formulation 1

The exponential integral function is the real function $E_1: \R_{>0} \to \R$ defined as:

$\map {E_1} x = \ds \int_{t \mathop = x}^{t \mathop \to +\infty} \frac {e^{-t} } t \rd t$

Formulation 2

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.