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//
// Copyright (C) 2009 - 2016 by the deal.II authors
//
// This file is part of the deal.II library.
//
// The deal.II library is free software; you can use it, redistribute
// it, and/or modify it under the terms of the GNU Lesser General
// Public License as published by the Free Software Foundation; either
// version 2.1 of the License, or (at your option) any later version.
// The full text of the license can be found in the file LICENSE at
// the top level of the deal.II distribution.
//
// ---------------------------------------------------------------------
#ifndef dealii__vector_view_h
#define dealii__vector_view_h
#include <deal.II/base/config.h>
#include <deal.II/base/exceptions.h>
#include <deal.II/base/subscriptor.h>
#include <deal.II/lac/vector.h>
#include <cstdio>
DEAL_II_NAMESPACE_OPEN
/*! @addtogroup Vectors
*@{
*/
/**
* View of a numerical vector of data. This class provides an interface
* compatible with the Vector<double> class (from which it is inherited), that
* allows fast access to locations of memory already allocated with arrays of
* type Number.
*
* This is in the same style of the vector view in the Trilinos library.
*
* You should consider using the VectorView object ONLY when ALL of the
* following requirements are met:
*
* 1. Your application requires a Vector<Number> object.
*
* 2. All you have at your disposal is a Number* pointer.
*
* 3. You are ABSOLUTELY SURE that the above pointer points to a valid area of
* memory of the correct size.
*
* 4. You really believe that making a copy of that memory would be too
* expensive.
*
* 5. You really know what you are doing.
*
* Notice that NO CHECKS are performed on the actual memory, and if you try to
* access illegal areas of memory, your computer will suffer from it. Once
* again, use this class ONLY if you know exactly what you are doing.
*
* Two constructors are provided. One for read-write access, and one for read
* only access, and you are allowed to use this class on objects of type const
* Number*. However you should be aware of the fact that the constness of the
* array pointed to is ignored, which means that you should only use the const
* constructor when the actual object you are constructing is itself a
* constant object. As a corollary, you will be allowed to call even functions
* of the base class that change data of the array; this being a violation of
* the C++ type model, you should make sure that this only happens if it is
* really valid and, in general, if you know what you are doing.
*
* Since this class does not own the memory that you are accessing, you have
* to make sure that the lifetime of the section of memory you are viewing is
* longer than this object. No attempt is made to ensure that this is the
* case.
*
* An example usage of this class is the following:
*
* @code
* // Create an array of length 5;
* double * array = new double[5];
* // Now create a view of the above array that is compatible with the
* // Vector<double> class
* VectorView<double> view(5, array);
*
* view(1) = 4;
*
* // The following line should output 4.
* cout << array[1] << endl;
*
* // If debug mode is on, then the following triggers an exception:
* view(6) = 4;
*
* // But notice that no checks are performed, so this is legal but WILL
* // NOT work
* VectorView<double> wrong_view(10, array);
*
* // Now no assert will be thrown if you type wrong_view(6), but most
* // likely a segfault will occur.
* view(6) = 4;
*
* // Notice that this construction is legal. It will create a copy of
* // the array.
* const Vector<double> const_copy(view);
*
* // Now this is the correct way to instantiate a constant view of the
* // above vector:
* const VectorView<double> correct_const_copy_view(5, const_copy.begin());
*
* // While this will compile, BUT WILL NOT COMPLAIN if you try to write
* // on it!
* VectorView<double> wrong_const_copy_view(5, const_copy.begin());
*
* // Now writing to elements of wrong_const_copy_view is allowed, and
* // will change the same memory as the const_copy object.
* wrong_const_copy_view(1) = 5;
*
* if(copy_view(1) == wrong_const_copy_view(1)) cout << "Tautology";
*
* @endcode
*
*
* @note Instantiations for this template are provided for <tt>@<float@>,
* @<double@>, @<long double@>, @<std::complex@<float@>@>,
* @<std::complex@<double@>@>, @<std::complex@<long double@>@></tt>; others
* can be generated in application programs (see the section on
* @ref Instantiations
* in the manual).
*
* @author Luca Heltai, 2009
*/
template<typename Number>
class VectorView : public Vector<Number>
{
public:
/**
* Declare type for container size.
*/
typedef types::global_dof_index size_type;
/**
* Read write constructor. Takes the size of the vector, just like the
* standard one, but the data is picked starting from the location of the
* pointer @p ptr.
*/
VectorView(const size_type new_size, Number *ptr);
/**
* The constant constructor is the same as above, however you will not be
* able to access the data for write access.
*
* You should only use this class by constructing it as a const
* VectorView<double>(size, ptr) object.
*
* Undefined behavior will occur if you construct it as a non const object
* or attempt to write on it.
*/
VectorView(const size_type new_size, const Number *ptr);
/**
* This destructor will only reset the internal sizes and the internal
* pointers, but it will NOT clear the memory.
*/
~VectorView();
/**
* The reinit function of this object has a behavior which is different from
* the one of the base class. VectorView does not handle memory, and you
* should not attempt to resize the memory that is pointed to by this object
* using the reinit function. You can, however, resize the view that you
* have of the original object. Notice that it is your own responsibility to
* ensure that the memory you are pointing to is big enough.
*
* Similarly to what happens in the base class, if 'omit_zeroing_entries' is
* false, then the entire content of the vector is set to 0, otherwise the
* content of the memory is left unchanged.
*
* Notice that the following snippet of code may not produce what you
* expect:
*
* @code
* // Create a vector of length 1.
* Vector<double> long_vector(1);
*
* // Make a view of it
* VectorView<double> view_of_long_vector(1, long_vector.begin());
*
* // Resize the original vector to a bigger size
* long_vector.reinit(100);
*
* // And the view, leaving the memory untouched
* view_of_long_vector.reinit(100, true);
* @endcode
*
* In the above case, the Vector<double>::reinit method is called, and a NEW
* area of memory is reserved, possibly not starting at the same place as
* before. However, the VectorView<double> object keeps pointing to the same
* old area. After the two reinits, any call to view_of_long_vector(i), with
* i>0 might cause an attempt to access invalid areas of memory, or might
* function properly, depending on whether or not the system was able to
* allocate some memory consecutively after the original allocation.
*
* In any case, you should not rely on this behavior, and you should only
* call this reinit function if you really know what you are doing.
*/
virtual void reinit (const size_type N,
const bool omit_zeroing_entries=false);
/**
* This reinit function is equivalent to constructing a new object with the
* given size, starting from the pointer ptr.
*/
void reinit(const size_type N, Number *ptr);
/**
* This reinit function is equivalent to constructing a new object with the
* given size, starting from the pointer ptr. The same considerations made
* for the constructor apply here.
*/
void reinit(const size_type N, const Number *ptr);
/**
* This function is here to prevent memory corruption. It should never be
* called, and will throw an exception if you try to do so.
*/
virtual void swap (Vector<Number> &v);
};
/*@}*/
/*----------------------- Inline functions ----------------------------------*/
#ifndef DOXYGEN
template<typename Number>
inline
VectorView<Number>::VectorView(const size_type new_size, Number *ptr)
{
this->vec_size = new_size;
this->max_vec_size = new_size;
this->val = ptr;
}
template<typename Number>
inline
VectorView<Number>::VectorView(const size_type new_size, const Number *ptr)
{
this->vec_size = new_size;
this->max_vec_size = new_size;
this->val = const_cast<Number *>(ptr);
}
template<typename Number>
inline
VectorView<Number>::~VectorView()
{
// avoid that the base class releases
// memory it doesn't own
this->vec_size = 0;
this->max_vec_size = 0;
this->val = 0;
}
template<typename Number>
inline
void VectorView<Number>::reinit(const size_type N,
const bool omit_zeroing_entries)
{
this->vec_size = N;
this->max_vec_size = N;
if (omit_zeroing_entries == false)
Vector<Number>::operator=(static_cast<Number>(0));
}
template<typename Number>
inline
void VectorView<Number>::reinit(const size_type new_size, Number *ptr)
{
this->vec_size = new_size;
this->max_vec_size = new_size;
this->val = ptr;
}
template<typename Number>
inline
void VectorView<Number>::reinit(const size_type new_size, const Number *ptr)
{
this->vec_size = new_size;
this->max_vec_size = new_size;
this->val = const_cast<Number *>(ptr);
}
template<typename Number>
inline
void VectorView<Number>::swap(Vector<Number> &)
{
AssertThrow(false, ExcMessage("Cant' swap a VectorView with a Vector!"));
}
#endif
DEAL_II_NAMESPACE_CLOSE
#endif
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