complex_monit can be used to return additional monitoring information during computation. It is in a suite of functions consisting of complex_init(), complex_iter(), complex_proc(), complex_option() and complex_monit.

For full information please refer to the NAG Library document for f12as

commdict, communication object

Communication structure.

This argument must have been initialized by a prior call to complex_init().


The number of the current Arnoldi iteration.


The number of converged eigenvalues so far.

ritzcomplex, ndarray, shape

The first locations of the array contain the converged approximate eigenvalues.

rzestcomplex, ndarray, shape

The first locations of the array contain the complex Ritz estimates on the converged approximate eigenvalues.


The suite of functions is designed to calculate some of the eigenvalues, , (and optionally the corresponding eigenvectors, ) of a standard complex eigenvalue problem , or of a generalized complex eigenvalue problem of order , where is large and the coefficient matrices and are sparse and complex. The suite can also be used to find selected eigenvalues/eigenvectors of smaller scale dense complex problems.

On an intermediate exit from complex_iter() with , complex_monit may be called to return monitoring information on the progress of the Arnoldi iterative process. The information returned by complex_monit is:

  • the number of the current Arnoldi iteration;

  • the number of converged eigenvalues at this point;

  • the converged eigenvalues;

  • the error bounds on the converged eigenvalues.

complex_monit does not have an equivalent function from the ARPACK package which prints various levels of detail of monitoring information through an output channel controlled via an argument value (see Lehoucq et al. (1998) for details of ARPACK routines). complex_monit should not be called at any time other than immediately following an return from complex_iter().


Lehoucq, R B, 2001, Implicitly restarted Arnoldi methods and subspace iteration, SIAM Journal on Matrix Analysis and Applications (23), 551–562

Lehoucq, R B and Scott, J A, 1996, An evaluation of software for computing eigenvalues of sparse nonsymmetric matrices, Preprint MCS-P547-1195, Argonne National Laboratory

Lehoucq, R B and Sorensen, D C, 1996, Deflation techniques for an implicitly restarted Arnoldi iteration, SIAM Journal on Matrix Analysis and Applications (17), 789–821

Lehoucq, R B, Sorensen, D C and Yang, C, 1998, ARPACK Users’ Guide: Solution of Large-scale Eigenvalue Problems with Implicitly Restarted Arnoldi Methods, SIAM, Philadelphia