NAG Library Function Document
nag_bessel_i1_scaled (s18cfc) returns a value of the scaled modified Bessel function .
||nag_bessel_i1_scaled (double x)
nag_bessel_i1_scaled (s18cfc) evaluates an approximation to , where is a modified Bessel function of the first kind. The scaling factor removes most of the variation in .
The function uses the same Chebyshev expansions as nag_bessel_i1 (s18afc)
, which returns the unscaled value of
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
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.
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 (s18cfce.c)
9.2 Program Data
Program Data (s18cfce.d)
9.3 Program Results
Program Results (s18cfce.r)