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//
// Copyright (C) 2009 - 2015 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__fe_block_mask_h
#define dealii__fe_block_mask_h
#include <deal.II/base/config.h>
#include <deal.II/base/exceptions.h>
#include <deal.II/base/memory_consumption.h>
#include <vector>
#include <iosfwd>
DEAL_II_NAMESPACE_OPEN
/**
* This class represents a mask that can be used to select individual vector
* blocks of a finite element (see also
* @ref GlossBlockMask "this glossary entry").
* It will typically have as many elements as the finite element has blocks,
* and one can use <code>operator[]</code> to query whether a particular block
* has been selected.
*
* The semantics of this class are the same as the related ComponentMask
* class, i.e., a default constructed mask represents all possible blocks. See
* there for more information about these semantics.
*
* Objects of this kind are used in many places where one wants to restrict
* operations to a certain subset of blocks, e.g. in DoFTools::extract_dofs.
* These objects can either be created by hand, or, simpler, by asking the
* finite element to generate a block mask from certain selected blocks using
* code such as this where we create a mask that only denotes the velocity
* block of a Stokes element (see
* @ref vector_valued):
* @code
* FESystem<dim> stokes_fe (FESystem<dim>(FE_Q<dim>(2), dim), 1, // Q2 element for the velocities
* FE_Q<dim>(1), 1); // Q1 element for the pressure
* FEValuesExtractors::Scalar pressure(dim);
* BlockMask pressure_mask = stokes_fe.block_mask (pressure);
* @endcode
* Note that by wrapping the velocity elements into a single FESystem object
* we make sure that the overall element has only 2 blocks. The result is a
* block mask that, in both 2d and 3d, would have values <code>[false,
* true]</code>. (Compare this to the corresponding component mask discussed
* in the ComponentMask documentation.) Similarly, using
* @code
* FEValuesExtractors::Vector velocities(0);
* BlockMask velocity_mask = stokes_fe.block_mask (velocities);
* @endcode
* would result in a mask <code>[true, false]</code> in both 2d and 3d.
*
* @ingroup fe
* @author Wolfgang Bangerth
* @date 2012
* @ingroup vector_valued
*/
class BlockMask
{
public:
/**
* Initialize a block mask. The default is that a block mask represents a
* set of blocks that are <i>all</i> selected, i.e., calling this
* constructor results in a block mask that always returns <code>true</code>
* whenever asked whether a block is selected.
*/
BlockMask ();
/**
* Initialize an object of this type with a set of selected blocks specified
* by the argument.
*
* @param block_mask A vector of <code>true/false</code> entries that
* determine which blocks of a finite element are selected. If the length of
* the given vector is zero, then this interpreted as the case where
* <i>every</i> block is selected.
*/
BlockMask (const std::vector<bool> &block_mask);
/**
* Initialize the block mask with a number of elements that are either all
* true or false.
*
* @param n_blocks The number of elements of this mask
* @param initializer The value each of these elements is supposed to have:
* either true or false.
*/
BlockMask (const unsigned int n_blocks,
const bool initializer);
/**
* If this block mask has been initialized with a mask of size greater than
* zero, then return the size of the mask represented by this object. On the
* other hand, if this mask has been initialized as an empty object that
* represents a mask that is true for every element (i.e., if this object
* would return true when calling represents_the_all_selected_mask()) then
* return zero since no definite size is known.
*/
unsigned int size () const;
/**
* Return whether a particular block is selected by this mask. If this mask
* represents the case of an object that selects <i>all blocks</i> (e.g. if
* it is created using the default constructor or is converted from an empty
* vector of type bool) then this function returns true regardless of the
* given argument.
*
* @param block_index The index for which the function should return whether
* the block is selected. If this object represents a mask in which all
* blocks are always selected then any index is allowed here. Otherwise, the
* given index needs to be between zero and the number of blocks that this
* mask represents.
*/
bool operator[] (const unsigned int block_index) const;
/**
* Return whether this block mask represents a mask with exactly
* <code>n</code> blocks. This is true if either it was initialized with a
* vector with exactly <code>n</code> entries of type <code>bool</code> (in
* this case, @p n must equal the result of size()) or if it was initialized
* with an empty vector (or using the default constructor) in which case it
* can represent a mask with an arbitrary number of blocks and will always
* say that a block is selected.
*/
bool
represents_n_blocks (const unsigned int n) const;
/**
* Return the number of blocks that are selected by this mask.
*
* Since empty block masks represent a block mask that would return
* <code>true</code> for every block, this function may not know the true
* size of the block mask and it therefore requires an argument that denotes
* the overall number of blocks.
*
* If the object has been initialized with a non-empty mask (i.e., if the
* size() function returns something greater than zero, or equivalently if
* represents_the_all_selected_mask() returns false) then the argument can
* be omitted and the result of size() is taken.
*/
unsigned int
n_selected_blocks (const unsigned int overall_number_of_blocks = numbers::invalid_unsigned_int) const;
/**
* Return the index of the first selected block. The argument is there for
* the same reason it exists with the n_selected_blocks() function.
*
* The function throws an exception if no block is selected at all.
*/
unsigned int
first_selected_block (const unsigned int overall_number_of_blocks = numbers::invalid_unsigned_int) const;
/**
* Return true if this mask represents a default constructed mask that
* corresponds to one in which all blocks are selected. If true, then the
* size() function will return zero.
*/
bool
represents_the_all_selected_mask () const;
/**
* Return a block mask that contains the union of the blocks selected by the
* current object and the one passed as an argument.
*/
BlockMask operator | (const BlockMask &mask) const;
/**
* Return a block mask that has only those elements set that are set both in
* the current object as well as the one passed as an argument.
*/
BlockMask operator & (const BlockMask &mask) const;
/**
* Return whether this object and the argument are identical.
*/
bool operator== (const BlockMask &mask) const;
/**
* Return whether this object and the argument are not identical.
*/
bool operator!= (const BlockMask &mask) const;
/**
* Determine an estimate for the memory consumption (in bytes) of this
* object.
*/
std::size_t
memory_consumption () const;
private:
/**
* The actual block mask.
*/
std::vector<bool> block_mask;
// make the output operator a friend so it can access
// the block_mask array
friend
std::ostream &operator << (std::ostream &out,
const BlockMask &mask);
};
/**
* Write a block mask to an output stream. If the block mask represents one
* where all blocks are selected without specifying a particular size of the
* mask, then it writes the string <code>[all blocks selected]</code> to the
* stream. Otherwise, it prints the block mask in a form like
* <code>[true,true,true,false]</code>.
*
* @param out The stream to write to.
* @param mask The mask to write. @return A reference to the first argument.
*/
std::ostream &operator << (std::ostream &out,
const BlockMask &mask);
// -------------------- inline functions ---------------------
inline
BlockMask::BlockMask()
{}
inline
BlockMask::BlockMask(const std::vector<bool> &block_mask)
:
block_mask (block_mask)
{}
inline
BlockMask::BlockMask(const unsigned int n_blocks,
const bool initializer)
:
block_mask (n_blocks, initializer)
{}
inline
unsigned int
BlockMask::size () const
{
return block_mask.size();
}
inline
bool
BlockMask::operator [](const unsigned int block_index) const
{
// if the mask represents the all-block mask
// then always return true
if (block_mask.size() == 0)
return true;
else
{
// otherwise check the validity of the index and
// return whatever is appropriate
Assert (block_index < block_mask.size(),
ExcIndexRange (block_index, 0, block_mask.size()));
return block_mask[block_index];
}
}
inline
bool
BlockMask::represents_n_blocks(const unsigned int n) const
{
return ((block_mask.size() == 0)
||
(block_mask.size() == n));
}
inline
unsigned int
BlockMask::n_selected_blocks(const unsigned int n) const
{
if ((n != numbers::invalid_unsigned_int) && (size() > 0))
AssertDimension (n, size());
const unsigned int real_n = (n != numbers::invalid_unsigned_int
?
n
:
size());
if (block_mask.size() == 0)
return real_n;
else
{
AssertDimension (real_n, block_mask.size());
unsigned int c = 0;
for (unsigned int i=0; i<block_mask.size(); ++i)
if (block_mask[i] == true)
++c;
return c;
}
}
inline
unsigned int
BlockMask::first_selected_block(const unsigned int n) const
{
if ((n != numbers::invalid_unsigned_int) && (size() > 0))
AssertDimension (n, size());
if (block_mask.size() == 0)
return 0;
else
{
for (unsigned int c=0; c<block_mask.size(); ++c)
if (block_mask[c] == true)
return c;
Assert (false, ExcMessage ("No block is selected at all!"));
return numbers::invalid_unsigned_int;
}
}
inline
bool
BlockMask::represents_the_all_selected_mask () const
{
return (block_mask.size() == 0);
}
inline
BlockMask
BlockMask::operator | (const BlockMask &mask) const
{
// if one of the two masks denotes the all-block mask,
// then return the other one
if (block_mask.size() == 0)
return mask;
else if (mask.block_mask.size() == 0)
return *this;
else
{
// if both masks have individual entries set, form
// the combination of the two
AssertDimension(block_mask.size(), mask.block_mask.size());
std::vector<bool> new_mask (block_mask.size());
for (unsigned int i=0; i<block_mask.size(); ++i)
new_mask[i] = (block_mask[i] || mask.block_mask[i]);
return new_mask;
}
}
inline
BlockMask
BlockMask::operator & (const BlockMask &mask) const
{
// if one of the two masks denotes the all-block mask,
// then return the other one
if (block_mask.size() == 0)
return mask;
else if (mask.block_mask.size() == 0)
return *this;
else
{
// if both masks have individual entries set, form
// the combination of the two
AssertDimension(block_mask.size(), mask.block_mask.size());
std::vector<bool> new_mask (block_mask.size());
for (unsigned int i=0; i<block_mask.size(); ++i)
new_mask[i] = (block_mask[i] && mask.block_mask[i]);
return new_mask;
}
}
inline
bool
BlockMask::operator== (const BlockMask &mask) const
{
return block_mask == mask.block_mask;
}
inline
bool
BlockMask::operator!= (const BlockMask &mask) const
{
return block_mask != mask.block_mask;
}
DEAL_II_NAMESPACE_CLOSE
#endif
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