On entry: ifail must be set to , or to set behaviour on detection of an error; these values have no effect when no error is detected.
A value of causes the printing of an error message and program execution will be halted; otherwise program execution continues. A value of means that an error message is printed while a value of means that it is not.
If halting is not appropriate, the value or is recommended. If message printing is undesirable, then the value is recommended. Otherwise, the value is recommended. When the value or is used it is essential to test the value of ifail on exit.
On exit: unless the routine detects an error or a warning has been flagged (see Section 6).
6Error Indicators and Warnings
If on entry or , explanatory error messages are output on the current error message unit (as defined by x04aaf).
Errors or warnings detected by the routine:
On entry, .
The routine has been called with an argument less than , for which is not defined.
An unexpected error has been triggered by this routine. Please
See Section 7 in the Introduction to the NAG Library FL Interface for further information.
Your licence key may have expired or may not have been installed correctly.
See Section 8 in the Introduction to the NAG Library FL Interface for further information.
Dynamic memory allocation failed.
See Section 9 in the Introduction to the NAG Library FL Interface for further information.
If and are the relative errors in the argument and result respectively, then in principle
That is the relative error in the argument is amplified by a factor at least in the result. The equality should apply if is greater than the machine precision ( due to data errors etc.) but if is simply a result of round-off in the machine representation it is possible that an extra figure may be lost in internal calculation and round-off. The behaviour of the amplification factor is shown in the following graph:
It should be noted that for the factor is always less than . For large we have the absolute error in the result, in principle, given by
This means that eventually accuracy is limited by machine precision. More significantly for close to , , the above analysis becomes inapplicable due to the fact that both function and argument are bounded, , . In this region we have
That is, there will be approximately half as many decimal places correct in the result as there were correct figures in the argument.
8Parallelism and Performance
s11acf is not threaded in any implementation.
This example reads values of the argument from a file, evaluates the function at each value of and prints the results.