s15af Method
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s15af returns a value for Dawson's Integral, Fx.

Syntax

C#
public static double s15af(
	double x
)
Visual Basic (Declaration)
Public Shared Function s15af ( _
	x As Double _
) As Double
Visual C++
public:
static double s15af(
	double x
)
F#
static member s15af : 
        x:float -> float

Parameters

x
Type: System..::.Double
On entry: the argument x of the function.

Return Value

s15af returns a value for Dawson's Integral, Fx.

Description

s15af evaluates an approximation for Dawson's Integral
Fx=e-x2∫0xet2dt.
The method is based on two Chebyshev expansions:
For 0<x≤4,
Fx=x∑r=0′arTrt,   where  t=2 x4 2-1.
For x>4,
Fx=1x∑r=0′brTrt,   where  t=2 4x 2-1.
For x near zero, Fx≃x, and for x large, Fx≃ 12x . These approximations are used for those values of x for which the result is correct to machine precision. For very large x on some machines, Fx may underflow and then the result is set exactly to zero (see the Library Constants section of the Introduction for details).

References

Error Indicators and Warnings

Accuracy

Further Comments

Example

See Also