nag_bessel_i_nu_scaled (s18ecc) returns the value of the scaled modified Bessel function  for real .

nag_bessel_i_nu_scaled (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 .

"NE_INT"

On entry, . Constraint: .

"NE_INTERNAL_ERROR"

An internal error has occurred in this function. Check the function call and any array sizes. If the call is correct then please consult NAG for assistance.

"NE_OVERFLOW_LIKELY"

The evaluation has been abandoned due to the likelihood of overflow. The result is returned as zero.

"NE_REAL_INT"

On entry, , . Constraint:  when .

"NE_TERMINATION_FAILURE"

The evaluation has been abandoned due to failure to satisfy the termination condition. The result is returned as zero.

"NE_TOTAL_PRECISION_LOSS"

The evaluation has been abandoned due to total loss of precision. The result is returned as zero.

"NW_SOME_PRECISION_LOSS"

The evaluation has been completed but some precision has been lost.

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.

None.