CHANGELOG

2024-02-20
cleanup the zdotc wrapper code

2024-02-09
added a C interface

2024-02-07
revised structure of drivers rs_diag and ch_diag to have a simpler
form of output.  (incompatible with earlier versions)	
minor fix to test_lanczos and
lanczos_iterator (mask feature)

2019-03-16:
use zdot_wrapper for  zdotc in vector_m when both
use_blas and wrap_zdotc are .true.

2019-03-11:
interface fixes for Blas functions zdotc etc.
intialise GAP to zero in lanczos_iterator

(cosmetic) fixed incorrect output when hermiticity test fails
2014-05-06:
now uses  a robust estimate for an upper bound to the gap to the next eigenvalue,
given by (vec, mat vec) where vec is a normalized starting vector that is
orthogonal to the previously-found eigenvectors.

2014-05-07
fixed a bug in tmatrix_m : in the rare accidental case that the reverse Cholesky decomposition
T - ev = LDU used in the Raleigh quotient iteration has exactly zero  in the last entry of D, the RQI
cannot  be used to improve the eigenvector.

2014-07-26
cleanup old style fortran (f77)  remnants in  tmatrix_m.f90
remove use of BLAS functions in tmatrix_m (use fortran95 equivalents)

2014-07-29  v3.0
Name changed to LANCZOS_ITERATOR.
Merged the real-symmetric and complex-hermitian cases by defining  a new  structure
TYPE (VECTOR_T) ) that can hold (as a pointer) either a real or a complex vector.

All vector manipulations are now extracted into module VECTOR_M,  which has a switch
USE_BLAS that can select between  using  the BLAS or the native fortran95 vector forms
for the basis linear algebra.   A module MATRIX_ALGEBRA_M now also provides an interface 
to LAPACK subprograms DSBTRD and DSTEBZ.

If BLAS is used, native fortran95 vector code can still be substituted for  the 
apparently-sometimes-broken ZDOTC by setting BROKEN_ZDOTC = .true.  (The use here of an 
explicit interface to ZDOTC may have cured any such problems.)
     
The basic Lanczos algorithms are now blind to whether the vector is real symmetric or 
complex Hermitian, and have no extrenal dependences.

A subprogram MATRIX_SUBSPACE_DETECTOR that can proble MATVEC for disconnected invariant 
subspaces is now also provided,in addition to LANCZOS_ITERATOR.