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, .
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.
Because of its close relationship with , the accuracy of this routine is very similar to that in s15adf. If and are the relative errors in result and argument, respectively, they are in principle related by
so that the relative error in the argument, , is amplified by a factor, , in the result.
For small and for positive this factor is always less than and accuracy is mainly limited by machine precision.
For large negative the factor behaves like and hence to a certain extent relative accuracy is unavoidably lost.
However, the absolute error in the result, , is given by
so absolute accuracy can be guaranteed for all .
8Parallelism and Performance
s15apf is not threaded in any implementation.
This example reads values of x from a file, evaluates the function at each value of and prints the results.