sin_integral

Definition:

$Si = sin\_integral(x)$ evaluates

$Si(x)=\int_0^x\frac{\sin u}udu$

The approximation is based on several Chebyshev expansions.

For more information please review the s13adc function in the NAG document.

x (input, double): The argument x of the function.
Si (output, double): the approximation of the formula $Si(x)=\int_0^x\frac{\sin u}udu$