s18ecc evaluates an approximation to the scaled modified Bessel function of the first kind
, where the order
or
and
is real and positive. For positive orders it may also be called with
, since
when
. For negative orders the formula
is used prior to multiplication by the scale factor
.
All constants in the underlying functions are specified to approximately 18 digits of precision. If denotes the number of digits of precision in the floating-point arithmetic being used, then clearly the maximum number of correct digits in the results obtained is limited by . Because of errors in argument reduction when computing elementary functions inside the underlying functions, the actual number of correct digits is limited, in general, by , where represents the number of digits lost due to the argument reduction. Thus the larger the value of , the less the precision in the result.
Background information to multithreading can be found in the
Multithreading documentation.
None.