=====
FLENS                                                                   [TOC]
=====

FLENS is short for _Flexible Library for Efficient Numerical Solutions_.  And
that's exactly what it is:

*A builing block for the implementation of other (higher-level) numerical
libraries or numerical applications*

Some key points

- C++ library (requires a C++11 conform compiler)
- Easy install as FLENS is *headers only*
- FLENS gives you
    - Matrix/vector types for dense linear algebra
    - Generic implementation of BLAS (see __CXXBLAS__)
    - Generic reimplementation of __LAPACK__ (see __FLENS-LAPACK__)
    - Generic implementation means that you can use any element type for
      your matrices/vectors that "acts like a double".  So in particular
      types from the __QD Library__,  __mpfr__, ...
- If high performance BLAS libraries like __ATLAS__/__GotoBLAS__/... are
  available you simply can link against them and boost performance.
- __FLENS-BLAS__ is a high-level and easy-to-use __BLAS__ interface
- __FLENS-LAPACK__ is a high-level and easy-to-use C++ implementation of
  __LAPACK__.
- FLENS also allows using overloaded operators for accessing BLAS.  Most
  important in this respect:
    - Overloaded operators come without performance penalty!
    - In a special debug mode you can exactly trace what is happening and
      how you linear algebra expressions gets evaluated through BLAS
      calls
    - More features are explained in the __tutorial__.


Examples and Tutorial
=====================

- Overview of all driver functions currently implemented in __FLENS-LAPACK__
- We just started with a __tutorial__:
    - __Session 1__: General matrices and dense vectors.
    - __Session 2__: BLAS, CXXBLAS, FLENS-BLAS and Overloaded Operators.
    - __Session 3__: More on matrices: Triangular and symmetric matrices,
      matrix views, ...
    - __Session 4__: Using FLENS-LAPACK.
    - __Session 5__: Using an external LAPACK implementation.
    - __Session 6__: Define your own matrix/vector types.
    - __Session 7__: How to define a *kick-ass interface* for FLENS-LAPACK.


Scope of this Branch
====================

- Only real matrix types with full storage and dense vector types, i.e.
    - __GeMatrix__,
    - __SyMatrix__,
    - __TrMatrix__,
    - __DenseVector__.
- Our generic BLAS implementation __CXXBLAS__.
- Support for high and multipecission types from __QD Library__ and __mpfr__.
- Support for native BLAS implementations like __ATLAS__ or __GotoBLAS__.
- __FLENS-BLAS__ and __FLENS-LAPACK__.
- Overloaded operators for BLAS working ontop of the __FLENS-BLAS__ layer.
- We improved our *doctool* (look at the bottom of each page for *document
  source*).  We now use *restructured text*.


Compiler Requirements
=====================
FLENS uses some of the C++11 features and therefore requires a recent C++
compiler:

  - __clang__ version 3.0 (or higher)
  - __gcc__ version 4.7 (or higher)
  - __icc__ version 12.1.2 (or higher)


Git It
======

You can clone a public branch from __GitHub__

  *--[BOX]------------------------------------------------------------------*
  |                                                                         |
  |  git clone git://github.com/michael-lehn/FLENS.git                      |
  |                                                                         |
  *-------------------------------------------------------------------------*

Philosophy
==========

  *--[BOX]------------------------------------------------------------------*
  |                                                                         |
  |  We are *FLENS*.                                                        |
  |                                                                         |
  |  Resistance is futile.                                                  |
  |                                                                         |
  |  Advanced technology will be assimilated...                             |
  |                                                                         |
  *-------------------------------------------------------------------------*

  This should answer the following questions:

  - Why are the matrix/vector types in FLENS as they are?
  - Why do we reimplement the LAPACK library with FLENS?
  - What is the idea behind our CXXBLAS?

  The answer is simple:

  - LAPACK is the most advanced and best supported numerical library in the
    world.  Improvements in numerical algorithms have a great chance to make
    it soon into LAPACK.  If we keep FLENS-LAPACK up-to-date to current LAPACK
    releases we keep up with some of the most sophisticated numerical
    algorithms.
  - LAPACK gains its performance from highly optimized BLAS kernel routines.
    These implementations achieve peak performance on certain platforms.
    When possible our CXXBLAS is just an interface to these implementations.
  - For multi-precision data types CXXBLAS gives you a generic implementation
    that does not give high performance (yet) but allows using LAPACK in
    high precision.


Mailing List
============

Join the mailing __list__!


:links: __FLENS-LAPACK__ -> doc:flens/lapack/lapack
        __FLENS-BLAS__   -> doc:flens/blas/blas
        __BLAS__         -> http://www.netlib.org/blas/
        __LAPACK__       -> http://www.netlib.org/lapack/
        __tutorial__     -> doc:flens/examples/tutorial
        __Session (\d)__ -> doc:flens/examples/tutorial#$1
        __GeMatrix__     -> file:flens/matrixtypes/general/impl/gematrix.h
        __SyMatrix__     -> file:flens/matrixtypes/symmetric/impl/symatrix.h
        __TrMatrix__     -> file:flens/matrixtypes/triangular/impl/trmatrix.h
        __DenseVector__  -> file:flens/vectortypes/impl/densevector.h
        __CXXBLAS__      -> dir:cxxblas/
        __QD Library__   -> http://crd-legacy.lbl.gov/~dhbailey/mpdist
        __mpfr__         -> http://www.mpfr.org
        __ATLAS__        -> http://math-atlas.sourceforge.net
        __GotoBLAS__     -> http://www.tacc.utexas.edu/tacc-projects/gotoblas2
        __GitHub__       -> http://github.com/michael-lehn/FLENS
        __clang__        -> http://clang.llvm.org/
        __gcc__          -> http://gcc.gnu.org/
        __icc__          -> http://software.intel.com/en-us/articles/intel-compilers/
        __list__         -> https://imap.uni-ulm.de/lists/info/flens