110 lines
4.2 KiB
C++
110 lines
4.2 KiB
C++
// This file is part of Eigen, a lightweight C++ template library
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// for linear algebra.
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//
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// Copyright (C) 2006-2008 Benoit Jacob <jacob.benoit.1@gmail.com>
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//
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// Eigen is free software; you can redistribute it and/or
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// modify it under the terms of the GNU Lesser General Public
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// License as published by the Free Software Foundation; either
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// version 3 of the License, or (at your option) any later version.
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//
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// Alternatively, you can redistribute it and/or
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// modify it under the terms of the GNU General Public License as
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// published by the Free Software Foundation; either version 2 of
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// the License, or (at your option) any later version.
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//
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// Eigen is distributed in the hope that it will be useful, but WITHOUT ANY
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// WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
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// FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public License or the
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// GNU General Public License for more details.
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//
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// You should have received a copy of the GNU Lesser General Public
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// License and a copy of the GNU General Public License along with
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// Eigen. If not, see <http://www.gnu.org/licenses/>.
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#ifndef EIGEN_EVAL_H
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#define EIGEN_EVAL_H
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/** \class Eval
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*
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* \brief Evaluation of an expression
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*
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* The template parameter Expression is the type of the expression that we are evaluating.
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*
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* This class is the return
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* type of MatrixBase::eval() and most of the time this is the only way it
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* is used.
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*
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* However, if you want to write a function returning an evaluation of an expression, you
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* will need to use this class.
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*
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* Here is an example illustrating this:
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* \include class_Eval.cpp
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* Output: \verbinclude class_Eval.out
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*
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* \sa MatrixBase::eval()
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*/
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template<typename ExpressionType>
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struct ei_traits<Eval<ExpressionType> >
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{
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typedef typename ExpressionType::Scalar Scalar;
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enum {
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RowsAtCompileTime = ExpressionType::RowsAtCompileTime,
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ColsAtCompileTime = ExpressionType::ColsAtCompileTime,
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MaxRowsAtCompileTime = ExpressionType::MaxRowsAtCompileTime,
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MaxColsAtCompileTime = ExpressionType::MaxColsAtCompileTime,
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Flags = ExpressionType::Flags & ~LazyBit
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};
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};
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template<typename ExpressionType> class Eval : ei_no_assignment_operator,
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public Matrix< typename ExpressionType::Scalar,
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ExpressionType::RowsAtCompileTime,
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ExpressionType::ColsAtCompileTime,
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ExpressionType::Flags,
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ExpressionType::MaxRowsAtCompileTime,
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ExpressionType::MaxColsAtCompileTime>
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{
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public:
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/** The actual matrix type to evaluate to. This type can be used independently
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* of the rest of this class to get the actual matrix type to evaluate and store
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* the value of an expression.
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*
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* Here is an example illustrating this:
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* \include Eval_MatrixType.cpp
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* Output: \verbinclude Eval_MatrixType.out
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*/
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typedef Matrix<typename ExpressionType::Scalar,
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ExpressionType::RowsAtCompileTime,
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ExpressionType::ColsAtCompileTime,
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ExpressionType::Flags,
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ExpressionType::MaxRowsAtCompileTime,
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ExpressionType::MaxColsAtCompileTime> MatrixType;
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_EIGEN_GENERIC_PUBLIC_INTERFACE(Eval, MatrixType)
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explicit Eval(const ExpressionType& expr) : MatrixType(expr) {}
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};
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/** Evaluates *this, which can be any expression, and returns the obtained matrix.
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*
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* A common use case for this is the following. In an expression-templates library
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* like Eigen, the coefficients of an expression are only computed as they are
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* accessed, they are not computed when the expression itself is constructed. This is
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* usually a good thing, as this "lazy evaluation" improves performance, but can also
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* in certain cases lead to wrong results and/or to redundant computations. In such
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* cases, one can restore the classical immediate-evaluation behavior by calling eval().
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*
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* Example: \include MatrixBase_eval.cpp
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* Output: \verbinclude MatrixBase_eval.out
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*
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* \sa class Eval */
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template<typename Derived>
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const typename ei_eval_unless_lazy<Derived>::type MatrixBase<Derived>::eval() const
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{
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return typename ei_eval_unless_lazy<Derived>::type(derived());
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}
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#endif // EIGEN_EVAL_H
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