public static double s18cf(
	double x
)

Public Shared Function s18cf ( _
	x As Double _
) As Double

public:
static double s18cf(
	double x
)

static member s18cf : 
        x : float -> float 

s18cf returns a value of the scaled modified Bessel function $e^{-\left|x\right|}{I}_1\left(x\right)$.

s18cf evaluates an approximation to $e^{-\left|x\right|}{I}_1\left(x\right)$, where $I_1$ is a modified Bessel function of the first kind. The scaling factor $e^{-\left|x\right|}$ removes most of the variation in $I_1\left(x\right)$.

The method uses the same Chebyshev expansions as s18af, which returns the unscaled value of $I_1\left(x\right)$.

Abramowitz M and Stegun I A (1972) Handbook of Mathematical Functions (3rd Edition) Dover Publications

There are no actual failure exits from this method. _ifail is always set to zero. This parameter is included for compatibility with other methods in this chapter.

Relative errors in the argument are attenuated when propagated into the function value. When the accuracy of the argument is essentially limited by the machine precision, the accuracy of the function value will be similarly limited by at most a small multiple of the machine precision.

None.

None.

This example reads values of the argument $x$ from a file, evaluates the function at each value of $x$ and prints the results.