Computes the principal value of the exponential integral.

Namespace: Meta.Numerics.Functions
Assembly: Meta.Numerics (in Meta.Numerics.dll) Version: 2.1.0.0 (2.1.0.0)

Syntax

            
 C#  Visual Basic  Visual C++  F# 
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

ExceptionCondition
System..::..ArgumentOutOfRangeExceptionx is negative.

See Also