A FORTRAN implementation of the non-Hermitian Lanczos procedure with look-ahead to cure breakdowns is available in QMRPACK [180]. The corresponding routine names are DULAL for double precision real and ZULAL for double precision complex. These routines first run the look-ahead Lanczos algorithm without re-biorthogonalization for a number of steps. They will then prompt the user for the number of eigenvalues to compute. In addition, the routine will also find the common eigenvalues in two successive runs for the identification test as described at the step (16) of Algorithm 7.13.
A set of MATLAB routines for implementing the adaptive block Lanczos method (ABLE) described in §7.9 can be used to implement Algorithm 7.13 by defining the block size as one at the initial step. Optional re-biorthogonalization schemes are available. An adaptive block size scheme is used for the treatment of (near) breakdown and/or multiple or closely clustered eigenvalues of interest.
For more information about this software, including how to access it, see the book's homepage, ETHOME.