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cppad_eigen.hpp¶
View page sourceEnable Use of Eigen Linear Algebra Package with CppAD¶
Syntax¶
include <cppad/example/cppad_eigen.hpp>Purpose¶
Enables the use of the eigen
linear algebra package with the type AD < Base > ; see
Using custom scalar types .
Example¶
The files eigen_array.cpp and eigen_det.cpp contain an example and test of this include file. They return true if they succeed and false otherwise.
CppAD Declarations¶
First declare some items that are defined by cppad.hpp:
namespace CppAD {
// AD<Base>
template <class Base> class AD;
// numeric_limits<Float>
template <class Float> class numeric_limits;
}
std Declarations¶
Next declare some template specializations in std namespace:
namespace std {
template <class Base> bool isinf(const CppAD::AD<Base> &x);
template <class Base> bool isfinite(const CppAD::AD<Base> &x);
template <class Base> bool isnan(const CppAD::AD<Base> &x);
}
Include Eigen/Core¶
Next define the eigen plugin and then include Eigen/Core:
# define EIGEN_MATRIXBASE_PLUGIN <cppad/example/eigen_plugin.hpp>
# include <Eigen/Core>
Eigen NumTraits¶
Eigen needs the following definitions, in the Eigen namespace,
to work properly with AD < Base > scalars:
namespace Eigen {
template <class Base> struct NumTraits< CppAD::AD<Base> >
{ // type that corresponds to the real part of an AD<Base> value
typedef CppAD::AD<Base> Real;
// type for AD<Base> operations that result in non-integer values
typedef CppAD::AD<Base> NonInteger;
// type to use for numeric literals such as "2" or "0.5".
typedef CppAD::AD<Base> Literal;
// type for nested value inside an AD<Base> expression tree
typedef CppAD::AD<Base> Nested;
enum {
// does not support complex Base types
IsComplex = 0 ,
// does not support integer Base types
IsInteger = 0 ,
// only support signed Base types
IsSigned = 1 ,
// must initialize an AD<Base> object
RequireInitialization = 1 ,
// computational cost of the corresponding operations
ReadCost = 1 ,
AddCost = 2 ,
MulCost = 2
};
// machine epsilon with type of real part of x
// (use assumption that Base is not complex)
static CppAD::AD<Base> epsilon(void)
{ return CppAD::numeric_limits< CppAD::AD<Base> >::epsilon(); }
// relaxed version of machine epsilon for comparison of different
// operations that should result in the same value
static CppAD::AD<Base> dummy_precision(void)
{ return 100. *
CppAD::numeric_limits< CppAD::AD<Base> >::epsilon();
}
// minimum normalized positive value
static CppAD::AD<Base> lowest(void)
{ return CppAD::numeric_limits< CppAD::AD<Base> >::min(); }
// maximum finite value
static CppAD::AD<Base> highest(void)
{ return CppAD::numeric_limits< CppAD::AD<Base> >::max(); }
// number of decimal digits that can be represented without change.
static int digits10(void)
{ return CppAD::numeric_limits< CppAD::AD<Base> >::digits10; }
// number of decimal digits necessary to uniquely represent values.
static int max_digits10(void)
{ return CppAD::numeric_limits< CppAD::AD<Base> >::max_digits10; }
// not a number
static CppAD::AD<Base> quiet_NaN(void)
{ return CppAD::numeric_limits< CppAD::AD<Base> >::quiet_NaN(); }
// positive infinite value
static CppAD::AD<Base> infinity(void)
{ return CppAD::numeric_limits< CppAD::AD<Base> >::infinity(); }
};
}
Eigen ScalarBinaryOpTraits¶
namespace Eigen {
// Inform Eigen that a binary operations between Base and AD<Base>
// are allowed and thate the return type is AD<Base>
template<typename Base, typename BinOp>
struct ScalarBinaryOpTraits<CppAD::AD<Base>, Base, BinOp>{
typedef CppAD::AD<Base> ReturnType;
};
template<typename Base, typename BinOp>
struct ScalarBinaryOpTraits<Base, CppAD::AD<Base>, BinOp>
{
typedef CppAD::AD<Base> ReturnType;
};
}
CppAD Namespace¶
Eigen needs the following definitions, in the CppAD namespace,
to work properly with AD < Base > scalars:
namespace CppAD {
// functions that return references
template <class Base> const AD<Base>& conj(const AD<Base>& x)
{ return x; }
template <class Base> const AD<Base>& real(const AD<Base>& x)
{ return x; }
// functions that return values (note abs is defined by cppad.hpp)
template <class Base> AD<Base> imag(const AD<Base>& x)
{ return CppAD::AD<Base>(0.); }
template <class Base> AD<Base> abs2(const AD<Base>& x)
{ return x * x; }
}
eigen_vector¶
The class CppAD::eigen_vector is a wrapper for Eigen column vectors
so that they are simple vectors .
To be specific, it converts Eigen::Index arguments and
return values to size_t .
namespace CppAD {
template <class Scalar>
class eigen_vector : public Eigen::Matrix<Scalar, Eigen::Dynamic, 1> {
private:
// base_class
typedef Eigen::Matrix<Scalar, Eigen::Dynamic, 1> base_class;
public:
// constructor
eigen_vector(size_t n) : base_class( Eigen::Index(n) )
{ }
eigen_vector(void) : base_class()
{ }
// operator[]
Scalar& operator[](size_t i)
{ return base_class::operator[]( Eigen::Index(i) ); }
const Scalar& operator[](size_t i) const
{ return base_class::operator[]( Eigen::Index(i) ); }
// size
size_t size(void) const
{ return size_t( base_class::size() ); }
// resize
void resize(size_t n)
{ base_class::resize( Eigen::Index(n) ); }
};
}
Include cppad.hpp¶
# include <cppad/cppad.hpp>
std Definitions¶
The definitions below use cppad.hpp. Note that Value function can only be used with a constant parameter argument.
namespace std {
template <class Base> bool isinf(const CppAD::AD<Base> &x)
{ return isinf(CppAD::Value( CppAD::Var2Par(x) ) ); }
template <class Base> bool isfinite(const CppAD::AD<Base> &x)
{ return isfinite(CppAD::Value( CppAD::Var2Par(x) ) ); }
template <class Base> bool isnan(const CppAD::AD<Base> &x)
{ return CppAD::isnan(CppAD::Value( CppAD::Var2Par(x) ) ); }
}