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+namespace Eigen {
+
+/** \page CustomizingEigen Advanced - Customizing/Extending Eigen
+
+Eigen2 can be extended in several ways, for instance, by defining global methods, \ref ExtendingMatrixBase "by adding custom methods to MatrixBase", adding support to \ref CustomScalarType "custom types" etc.
+
+\b Table \b of \b contents
+  - \ref ExtendingMatrixBase
+  - \ref CustomScalarType
+  - \ref PreprocessorDirectives
+
+\section ExtendingMatrixBase Extending MatrixBase
+
+In this section we will see how to add custom methods to MatrixBase. Since all expressions and matrix types inherit MatrixBase, adding a method to MatrixBase make it immediately available to all expressions ! A typical use case is, for instance, to make Eigen compatible with another API.
+
+You certainly know that in C++ it is not possible to add methods to an extending class. So how that's possible ? Here the trick is to include in the declaration of MatrixBase a file defined by the preprocessor token \c EIGEN_MATRIXBASE_PLUGIN:
+\code
+class MatrixBase {
+  // ...
+  #ifdef EIGEN_MATRIXBASE_PLUGIN
+  #include EIGEN_MATRIXBASE_PLUGIN
+  #endif
+};
+\endcode
+Therefore to extend MatrixBase with you own methods you just have to create a file with your method declaration and define EIGEN_MATRIXBASE_PLUGIN before you include any Eigen's header file.
+
+Here is an example of such an extension file: \n
+\b MatrixBaseAddons.h
+\code
+inline Scalar at(uint i, uint j) const { return this->operator()(i,j); }
+inline Scalar& at(uint i, uint j) { return this->operator()(i,j); }
+inline Scalar at(uint i) const { return this->operator[](i); }
+inline Scalar& at(uint i) { return this->operator[](i); }
+
+inline RealScalar squaredLength() const { return squaredNorm(); }
+inline RealScalar length() const { return norm(); }
+inline RealScalar invLength(void) const { return fast_inv_sqrt(squaredNorm()); }
+
+template<typename OtherDerived>
+inline Scalar squaredDistanceTo(const MatrixBase<OtherDerived>& other) const
+{ return (derived() - other.derived()).squaredNorm(); }
+
+template<typename OtherDerived>
+inline RealScalar distanceTo(const MatrixBase<OtherDerived>& other) const
+{ return ei_sqrt(derived().squaredDistanceTo(other)); }
+
+inline void scaleTo(RealScalar l) { RealScalar vl = norm(); if (vl>1e-9) derived() *= (l/vl); }
+
+inline Transpose<Derived> transposed() {return transpose();}
+inline const Transpose<Derived> transposed() const {return transpose();}
+
+inline uint minComponentId(void) const  { int i; minCoeff(&i); return i; }
+inline uint maxComponentId(void) const  { int i; maxCoeff(&i); return i; }
+
+template<typename OtherDerived>
+void makeFloor(const MatrixBase<OtherDerived>& other) { derived() = derived().cwise().min(other.derived()); }
+template<typename OtherDerived>
+void makeCeil(const MatrixBase<OtherDerived>& other) { derived() = derived().cwise().max(other.derived()); }
+
+const typename Cwise<Derived>::ScalarAddReturnType
+operator+(const Scalar& scalar) const { return cwise() + scalar }
+
+friend const typename Cwise<Derived>::ScalarAddReturnType
+operator+(const Scalar& scalar, const MatrixBase<Derived>& mat) { return mat + scalar; }
+\endcode
+
+Then one can the following declaration in the config.h or whatever prerequisites header file of his project:
+\code
+#define EIGEN_MATRIXBASE_PLUGIN "MatrixBaseAddons.h"
+\endcode
+
+
+
+\section CustomScalarType Using custom scalar types
+
+By default, Eigen currently supports the following scalar types: \c int, \c float, \c double, \c std::complex<float>, \c std::complex<double>, \c long \c double, \c long \c long \c int (64 bits integers), and \c bool. The \c long \c double is especially useful on x86-64 systems or when the SSE2 instruction set is enabled because it enforces the use of x87 registers with extended accuracy.
+
+In order to add support for a custom type \c T you need:
+ 1 - make sure the common operator (+,-,*,/,etc.) are supported by the type \c T
+ 2 - add a specialization of struct Eigen::NumTraits<T> (see \ref NumTraits)
+ 3 - define a couple of math functions for your type such as: ei_sqrt, ei_abs, etc...
+     (see the file Eigen/src/Core/MathFunctions.h)
+
+Here is a concrete example adding support for the Adolc's \c adouble type. <a href="http://www.math.tu-dresden.de/~adol-c/">Adolc</a> is an automatic differentiation library. The type \c adouble is basically a real value tracking the values of any number of partial derivatives.
+
+\code
+#ifndef ADLOCSUPPORT_H
+#define ADLOCSUPPORT_H
+
+#define ADOLC_TAPELESS
+#include <adolc/adouble.h>
+#include <Eigen/Core>
+
+namespace Eigen {
+
+template<> struct NumTraits<adtl::adouble>
+{
+  typedef adtl::adouble Real;
+  typedef adtl::adouble FloatingPoint;
+  enum {
+    IsComplex = 0,
+    HasFloatingPoint = 1,
+    ReadCost = 1,
+    AddCost = 1,
+    MulCost = 1
+  };
+};
+
+}
+
+// the Adolc's type adouble is defined in the adtl namespace
+// therefore, the following ei_* functions *must* be defined
+// in the same namespace
+namespace adtl {
+
+  inline const adouble& ei_conj(const adouble& x)  { return x; }
+  inline const adouble& ei_real(const adouble& x)  { return x; }
+  inline adouble ei_imag(const adouble&)    { return 0.; }
+  inline adouble ei_abs(const adouble&  x)  { return fabs(x); }
+  inline adouble ei_abs2(const adouble& x)  { return x*x; }
+  inline adouble ei_sqrt(const adouble& x)  { return sqrt(x); }
+  inline adouble ei_exp(const adouble&  x)  { return exp(x); }
+  inline adouble ei_log(const adouble&  x)  { return log(x); }
+  inline adouble ei_sin(const adouble&  x)  { return sin(x); }
+  inline adouble ei_cos(const adouble&  x)  { return cos(x); }
+  inline adouble ei_pow(const adouble& x, adouble y)  { return pow(x, y); }
+
+}
+
+#endif // ADLOCSUPPORT_H
+\endcode
+
+
+
+\section PreprocessorDirectives Preprocessor directives
+
+You can control some aspects of Eigen by defining the following preprocessor tokens them before including any of Eigen's headers.
+ - \b EIGEN_NO_DEBUG disables Eigen assertions. Like NDEBUG but only affects Eigen's assertions.
+ - \b EIGEN_DONT_VECTORIZE disables explicit vectorization when defined.
+ - \b EIGEN_UNROLLING_LIMIT defines the maximal instruction counts to enable meta unrolling of loops. Set it to zero to disable unrolling. The default is 100.
+ - \b EIGEN_DEFAULT_TO_ROW_MAJOR the default storage order for matrices becomes row-major instead of column-major.
+ - \b EIGEN_TUNE_FOR_CPU_CACHE_SIZE represents the maximal size in Bytes of L2 blocks. Since several blocks have to stay concurently in L2 cache, this value should correspond to at most 1/4 of the size of L2 cache.
+ - \b EIGEN_NO_STATIC_ASSERT replaces compile time static assertions by runtime assertions
+ - \b EIGEN_MATRIXBASE_PLUGIN see \ref ExtendingMatrixBase
+
+*/
+
+}