On entry: IFAIL must be set to , . If you are unfamiliar with this parameter you should refer to Section 3.3 in the Essential Introduction for details.
For environments where it might be inappropriate to halt program execution when an error is detected, the value is recommended. If the output of error messages is undesirable, then the value is recommended. Otherwise, if you are not familiar with this parameter, the recommended value is . When the value 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).
6 Error 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:
The accuracy of the absolute error estimate ABSERR varies considerably with the type of sequence to which the routine is applied. In general it is better when applied to oscillating sequences than to monotonic sequences where it may be a severe underestimate.
8 Further Comments
The time taken is approximately proportional to the final value of NCALL.
For long sequences, a ‘window’ of the last values can be used instead of all the terms of the sequence. Tests on a variety of problems indicate that a suitable value is ; this implies a value for LWORK of . You are advised to experiment with other values for your own specific problems.
C06BAF will induce convergence in some divergent sequences. See Shanks (1955) for more details.