README_ZDOTC

The BLAS (Basic Linear Algebra Subprograms) library that
comes with LAPACK is used by default, as it may be 
available in an architecture-optimized form.

Use of BLAS can be disabled (before calling lanczos) by a call
    
    call set_use_blas(.false.)    (Fortran)
    set_use_blas(false);          (C with #include <stdbool.h>)
    set_use_blas(0);              (C)

Native Fortran95 vector procedures will then be used instead.
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Some compilers (e.g. gfortran) may by default produce code
not compatible with LAPACK/BLAS implementations of the
double complex function ZDOTC, such as those in Intel MKL
or Apple VecLib. This is because an incompatible convention
for the return values of complex functions is being used.

This can be tested for by compiling and running the program
test_zdotc.f90, after linking it with the desired BLAS implementation.

If this shows that this compiler/library combination breaks ZDOTC, the
solution is to call the wrapper ZDOTC_WRAPPER instead of calling ZDOTC.

Use of the wrapper is activated by a call (before calling lanczos)
    
    call set_wrap_zdotc(.true.)   (Fortran)
    set_wrap_zdotc(true);         (C with #include <stdbool.h>)
    set_wrap_zdotc(1);            (C)