f11bff is the third in a suite of three routines for the iterative solution of a real general (nonsymmetric) system of simultaneous linear equations (see Golub and Van Loan (1996)). f11bff returns information about the computations during an iteration and/or after this has been completed. The first routine of the suite, f11bdf, is a setup routine; the second routine, f11bef, is the iterative solver itself.
These three routines are suitable for the solution of large sparse general (nonsymmetric) systems of equations.
The routine may be called by the names f11bff or nagf_sparse_real_gen_basic_diag.
f11bff returns information about the solution process. It can be called either during a monitoring step of f11bef or after f11bef has completed its tasks. Calling f11bff at any other time will result in an error condition being raised.
For further information you should read the documentation for f11bdfandf11bef.
Golub G H and Van Loan C F (1996) Matrix Computations (3rd Edition) Johns Hopkins University Press, Baltimore
1: – IntegerOutput
On exit: the number of iterations carried out by f11bef.
2: – Real (Kind=nag_wp)Output
On exit: the current value of the left-hand side of the termination criterion used by f11bef.
3: – Real (Kind=nag_wp)Output
On exit: the current value of the right-hand side of the termination criterion used by f11bef.
4: – Real (Kind=nag_wp)Output
On exit: if in the previous call to f11bdf, then anorm contains , where , or , either supplied or, in the case of or , estimated by f11bef; otherwise .
5: – Real (Kind=nag_wp)Output
On exit: if in the previous call to f11bdf, the current estimate of the largest singular value of the preconditioned iteration matrix, either when it has been supplied to f11bdf or it has been estimated by f11bef (see also Sections 3 and 5 in f11bdf); otherwise, is returned.
On entry: the dimension of the array work as declared in the (sub)program from which f11bff is called (see also Section 5 in f11bdf).
Note: although the minimum value of lwork ensures the correct functioning of f11bff, a larger value is required by the iterative solver f11bef (see also Section 5 in f11bdf).
8: – IntegerInput/Output
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:
f11bff has been called out of sequence.
On entry, . Constraint: .
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.
8Parallelism and Performance
Background information to multithreading can be found in the Multithreading documentation.