IntegralEi Method (x)

Computes the principal value of the exponential integral.

Declaration Syntax

Visual Basic

Visual C++

public static double IntegralEi(
	double x
)

Public Shared Function IntegralEi ( _
	x As Double _
) As Double

public:
static double IntegralEi(
	double x
)

static member IntegralEi : 
        x:float -> float

Parameters

x (Double): The argument, which must be non-negative.

Return Value

The value of Ei(x).

Remarks

The function Ei(x) appears in the evaluation of some indefinite integrals involving exponents and in number theory in the approximation li(x) = Ei(ln x) to the cumulative distribution of primes.

It is related to the real part of the exponential integral for negative arguments by E₁(-x ± iε) = -Ei(x) ∓ iπ.

Exceptions

Exception	Condition
ArgumentOutOfRangeException	x is negative.