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Using FLENS-LAPACK as CXXLAPACK Font-End                                  [TOC]
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FLENS-LAPACK not only provides a generic implementation for a set of certain
LAPACK functions.  It also serves as a high-level interface for CXXLAPACK.  In
this respect it follows the ideas introduced on the previous pages.


Generic or External LAPACK:  How to select?
===========================================
Consider a LAPACK function like `xGETRF`.  In FLENS-LAPACK we provide its
functionality through the routine `lapack::trf`.  Using macros you can control
whether it calls a generic implementation or an external LAPACK implementation:

- By default and if possible FLENS-LAPACK will always call the generic
  implementation of a LAPACK routine.
- If the `USE_CXXLAPACK` macro is defined *and* no generic implementation is
  available then the external implementation gets called.  This happens through
  the CXXLAPCK layer.
- If the `ALWAYS_USE_CXXLAPACK` macro is defined then all FLENS-LAPACK routines
  will delegate functionality to the external LAPACK implementation.  If you
  define this macro then the `USE_CXXLAPACK` gets automatically defined (see
  __lapack-header__).

You can be even more selective.  For each function call you can explicitly
specify whether the generic or external function gets called:

- `lapack::generic::trf_impl` is the generic implementation of `lapack::trf` and
- `lapack::external::trf_impl` is a high-level interface for `cxxlapack::getrf`.


:links:  __lapack-header__  -> file:flens/lapack/lapack.h


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