x04aaf enables those Library routines which output error messages, to determine the number of the output unit to which the error messages are to be sent; in this case x04aaf is called with

iflag = 0

. x04aaf may also be called with

iflag = 1

to set the unit number to a specified value. Otherwise a default value (stated in the Users' Note for your implementation) is returned.

Records written to this output unit by other Library routines are at most

80

characters long (including a line-printer carriage control character).

Note that if the unit number is set

< 0

, no messages will be output.

4 References

None.

5 Arguments

1: $iflag$ – Integer Input: On entry: the action to be taken (see nerr).

Constraint: $iflag = 0$ or $1$ .
2: $nerr$ – Integer Input/Output: On entry: if $iflag = 0$ , nerr need not be set.
If $iflag = 1$ , nerr must specify the new error message unit number.

On exit: if $iflag = 0$ , nerr is set to the current error message unit number.
If $iflag = 1$ , nerr is unchanged.

Note that Fortran unit numbers must be positive or zero. If nerr is set $< 0$ , output of error messages is totally suppressed. It is important to note that if you supply an illegal value for nerr (such as a unit number associated with a file opened for reading instead of writing) then x04aaf cannot detect that fact, but any output sent to the unit by later calls of NAG routines may have undesirable consequences, such as program crashes.

6 Error Indicators and Warnings

None.

7 Accuracy

Not applicable.

8 Parallelism and Performance

Background information to multithreading can be found in the Multithreading documentation.

x04aaf is not thread safe and should not be called from a multithreaded user program. Please see Section 1 in FL Interface Multithreading for more information on thread safety.

x04aaf is not threaded in any implementation.

9 Further Comments

The time taken by x04aaf is negligible.

10 Example

In this example x04aaf is called by your main program to make the error message from the routine DUMMY appear on the same unit as the rest of the output (unit

6

). Normally a NAG Library routine with an IFAIL argument (see Section 4.2 in the Introduction to the NAG Library FL Interface) would take the place of DUMMY.