nag_airy_bi_deriv (s17akc) returns a value of the derivative of the Airy function .

nag_airy_bi_deriv (s17akc) calculates an approximate value for the derivative of the Airy function . It is based on a number of Chebyshev expansions.

For large negative arguments, it is impossible to calculate a result for the oscillating function with any accuracy so the function evaluation must fail. This occurs for , where  is the machine precision.

For large positive arguments, where  grows in an essentially exponential manner, there is a danger of overflow so the function must fail.

"NE_REAL_ARG_GT"

On entry, x must not be greater than : . x is too large and positive. The function returns zero.

"NE_REAL_ARG_LT"

On entry, x must not be less than : . x is too large and negative. The function returns zero.

For negative arguments the function is oscillatory and hence absolute error is appropriate. In the positive region the function has essentially exponential behaviour and hence relative error is needed. The absolute error, , and the relative error , are related in principle to the relative error in the argument , by , .

In practice, approximate equality is the best that can be expected. When ,  or  is of the order of the machine precision, the errors in the result will be somewhat larger.

For small , positive or negative, errors are strongly attenuated by the function and hence will effectively be bounded by the machine precision.

For moderate to large negative , the error is, like the function, oscillatory. However, the amplitude of the absolute error grows like . Therefore it becomes impossible to calculate the function with any accuracy if .

For large positive , the relative error amplification is considerable: . However, very large arguments are not possible due to the danger of overflow. Thus in practice the actual amplification that occurs is limited.

None.