NAG Library Function Document
nag_sin_integral (s13adc) returns the value of the sine integral .
||nag_sin_integral (double x)
nag_sin_integral (s13adc) evaluates
The approximation is based on several Chebyshev expansions.
Abramowitz M and Stegun I A (1972) Handbook of Mathematical Functions (3rd Edition) Dover Publications
x – doubleInput
On entry: the argument of the function.
6 Error Indicators and Warnings
If and are the relative errors in the argument and result, respectively, then in principle . The equality may hold if is greater than the machine precision ( due to data errors etc.), but if is simply due to round-off in the machine representation, then since the factor relating to is always less than one, the accuracy will be limited by machine precision.
For , where is a machine-dependent value, to within machine precision.
The following program reads values of the argument from a file, evaluates the function at each value of and prints the results.
9.1 Program Text
Program Text (s13adce.c)
9.2 Program Data
Program Data (s13adce.d)
9.3 Program Results
Program Results (s13adce.r)