cell_base.hh
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cell_base.hh
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	/**
	* @file cell_base.hh
	*
	* @author Till Junge <till.junge@epfl.ch>
	*
	* @date 01 Nov 2017
	*
	* @brief Base class representing a unit cell cell with single
	* projection operator
	*
	* Copyright © 2017 Till Junge
	*
	* µSpectre is free software; you can redistribute it and/or
	* modify it under the terms of the GNU General Public License as
	* published by the Free Software Foundation, either version 3, or (at
	* your option) any later version.
	*
	* µSpectre is distributed in the hope that it will be useful, but
	* WITHOUT ANY WARRANTY; without even the implied warranty of
	* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
	* General Public License for more details.
	*
	* You should have received a copy of the GNU General Public License
	* along with GNU Emacs; see the file COPYING. If not, write to the
	* Free Software Foundation, Inc., 59 Temple Place - Suite 330,
	* Boston, MA 02111-1307, USA.
	*/

	#ifndef CELL_BASE_H
	#define CELL_BASE_H

	#include "common/common.hh"
	#include "common/ccoord_operations.hh"
	#include "common/field.hh"
	#include "common/utilities.hh"
	#include "materials/material_base.hh"
	#include "fft/projection_base.hh"
	#include "cell/cell_traits.hh"

	#include <vector>
	#include <memory>
	#include <tuple>
	#include <functional>
	#include <array>

	namespace muSpectre {
	/**
	* Cell adaptors implement the matrix-vector multiplication and
	* allow the system to be used like a sparse matrix in
	* conjugate-gradient-type solvers
	*/
	template <class Cell>
	class CellAdaptor;

	/**
	* Base class for cells that is not templated and therefore can be
	* in solvers that see cells as runtime-polymorphic objects. This
	* allows the use of standard
	* (i.e. spectral-method-implementation-agnostic) solvers, as for
	* instance the scipy solvers
	*/

	class Cell
	{
	public:
	//! sparse matrix emulation
	using Adaptor = CellAdaptor<Cell>;

	//! dynamic vector type for interactions with numpy/scipy/solvers etc.
	using Vector_t = Eigen::Matrix<Real, Eigen::Dynamic, 1>;

	//! dynamic matrix type for setting strains
	using Matrix_t = Eigen::Matrix<Real, Eigen::Dynamic, Eigen::Dynamic>;

	//! ref to constant vector
	using ConstVector_ref = Eigen::Map<const Vector_t>;

	//! output vector reference for solvers
	using Vector_ref = Eigen::Map<Vector_t>;

	//! Default constructor
	Cell() = default;

	//! Copy constructor
	Cell(const Cell &other) = default;

	//! Move constructor
	Cell(Cell &&other) = default;

	//! Destructor
	virtual ~Cell() = default;

	//! Copy assignment operator
	Cell& operator=(const Cell &other) = default;

	//! Move assignment operator
	Cell& operator=(Cell &&other) = default;

	//! for handling double initialisations right
	bool is_initialised() const {return this->initialised;}

	//! returns the number of degrees of freedom in the cell
	virtual Dim_t get_nb_dof() const = 0;

	//! return the communicator object
	virtual const Communicator & get_communicator() const = 0;

	/**
	* formulation is hard set by the choice of the projection class
	*/
	virtual const Formulation & get_formulation() const = 0;

	/**
	* returns the material dimension of the problem
	*/
	virtual Dim_t get_material_dim() const = 0;

	/**
	* returns the number of rows and cols for the strain matrix type
	* (for full storage, the strain is stored in material_dim ×
	* material_dim matrices, but in symmetriy storage, it is a column
	* vector)
	*/
	virtual std::array<Dim_t, 2> get_strain_shape() const = 0;

	/**
	* returns a writable map onto the strain field of this cell. This
	* corresponds to the unknowns in a typical solve cycle.
	*/
	virtual Vector_ref get_strain_vector() = 0;

	/**
	* returns a read-only map onto the stress field of this
	* cell. This corresponds to the intermediate (and finally, total)
	* solution in a typical solve cycle
	*/
	virtual ConstVector_ref get_stress_vector() const = 0;


	/**
	* evaluates and returns the stress for the currently set strain
	*/
	virtual ConstVector_ref evaluate_stress() = 0;

	/**
	* evaluates and returns the stress and stiffness for the currently set strain
	*/
	virtual std::array<ConstVector_ref, 2> evaluate_stress_tangent() = 0;


	/**
	* applies the projection operator in-place on the input vector
	*/
	virtual void apply_projection(Eigen::Ref<Vector_t> vec) = 0;

	/**
	* freezes all the history variables of the materials
	*/
	virtual void save_history_variables() = 0;

	/**
	* evaluates the directional and projected stiffness (this
	* corresponds to G:K:δF in de Geus 2017,
	* http://dx.doi.org/10.1016/j.cma.2016.12.032). It seems that
	* this operation needs to be implemented with a copy in oder to
	* be compatible with scipy and EigenCG etc (At the very least,
	* the copy is only made once)
	*/
	virtual Vector_ref evaluate_projected_directional_stiffness
	(Eigen::Ref<const Vector_t> delF) = 0;


	/**
	* set uniform strain (typically used to initialise problems
	*/
	virtual void set_uniform_strain(const Eigen::Ref<const Matrix_t> &) = 0;

	//! get a sparse matrix view on the cell
	virtual Adaptor get_adaptor() = 0;
	protected:
	bool initialised{false}; //!< to handle double initialisation right

	private:
	};
	//! DimS spatial dimension (dimension of problem
	//! DimM material_dimension (dimension of constitutive law)
	template <Dim_t DimS, Dim_t DimM=DimS>
	class CellBase: public Cell
	{
	public:
	using Parent = Cell;
	using Ccoord = Ccoord_t<DimS>; //!< cell coordinates type
	using Rcoord = Rcoord_t<DimS>; //!< physical coordinates type
	//! global field collection
	using FieldCollection_t = GlobalFieldCollection<DimS>;
	//! the collection is handled in a `std::unique_ptr`
	using Collection_ptr = std::unique_ptr<FieldCollection_t>;
	//! polymorphic base material type
	using Material_t = MaterialBase<DimS, DimM>;
	//! materials handled through `std::unique_ptr`s
	using Material_ptr = std::unique_ptr<Material_t>;
	//! polymorphic base projection type
	using Projection_t = ProjectionBase<DimS, DimM>;
	//! projections handled through `std::unique_ptr`s
	using Projection_ptr = std::unique_ptr<Projection_t>;
	//! expected type for strain fields
	using StrainField_t =
	TensorField<FieldCollection_t, Real, secondOrder, DimM>;
	//! expected type for stress fields
	using StressField_t =
	TensorField<FieldCollection_t, Real, secondOrder, DimM>;
	//! expected type for tangent stiffness fields
	using TangentField_t =
	TensorField<FieldCollection_t, Real, fourthOrder, DimM>;
	//! combined stress and tangent field
	using FullResponse_t =
	std::tuple<const StressField_t&, const TangentField_t&>;
	//! iterator type over all cell pixel's
	using iterator = typename CcoordOps::Pixels<DimS>::iterator;

	//! dynamic vector type for interactions with numpy/scipy/solvers etc.
	using Vector_t = typename Parent::Vector_t;

	//! ref to constant vector
	using ConstVector_ref = typename Parent::ConstVector_ref;

	//! output vector reference for solvers
	using Vector_ref = typename Parent::Vector_ref;


	//! sparse matrix emulation
	using Adaptor = Parent::Adaptor;

	//! Default constructor
	CellBase() = delete;

	//! constructor using sizes and resolution
	CellBase(Projection_ptr projection);

	//! Copy constructor
	CellBase(const CellBase &other) = delete;

	//! Move constructor
	CellBase(CellBase &&other) = default;

	//! Destructor
	virtual ~CellBase() = default;

	//! Copy assignment operator
	CellBase& operator=(const CellBase &other) = delete;

	//! Move assignment operator
	CellBase& operator=(CellBase &&other) = default;

	/**
	* Materials can only be moved. This is to assure exclusive
	* ownership of any material by this cell
	*/
	Material_t & add_material(Material_ptr mat);


	/**
	* returns a writable map onto the strain field of this cell. This
	* corresponds to the unknowns in a typical solve cycle.
	*/
	virtual Vector_ref get_strain_vector() override;

	/**
	* returns a read-only map onto the stress field of this
	* cell. This corresponds to the intermediate (and finally, total)
	* solution in a typical solve cycle
	*/
	virtual ConstVector_ref get_stress_vector() const override;

	/**
	* evaluates and returns the stress for the currently set strain
	*/
	virtual ConstVector_ref evaluate_stress() override;

	/**
	* evaluates and returns the stress and stiffness for the currently set strain
	*/
	virtual std::array<ConstVector_ref, 2> evaluate_stress_tangent() override;


	/**
	* evaluates the directional and projected stiffness (this
	* corresponds to G:K:δF in de Geus 2017,
	* http://dx.doi.org/10.1016/j.cma.2016.12.032). It seems that
	* this operation needs to be implemented with a copy in oder to
	* be compatible with scipy and EigenCG etc. (At the very least,
	* the copy is only made once)
	*/
	virtual Vector_ref evaluate_projected_directional_stiffness
	(Eigen::Ref<const Vector_t> delF) override;

	//! return the template param DimM (required for polymorphic use of `Cell`
	Dim_t get_material_dim() const override final {return DimM;}

	/**
	* returns the number of rows and cols for the strain matrix type
	* (for full storage, the strain is stored in material_dim ×
	* material_dim matrices, but in symmetriy storage, it is a column
	* vector)
	*/
	std::array<Dim_t, 2> get_strain_shape() const override final;

	/**
	* applies the projection operator in-place on the input vector
	*/
	void apply_projection(Eigen::Ref<Vector_t> vec) override final;



	/**
	* set uniform strain (typically used to initialise problems
	*/
	void set_uniform_strain(const Eigen::Ref<const Matrix_t> &) override;


	/**
	* evaluates all materials
	*/
	FullResponse_t evaluate_stress_tangent(StrainField_t & F);

	/**
	* evaluate directional stiffness (i.e. G:K:δF or G:K:δε)
	*/

	StressField_t & directional_stiffness(const TangentField_t & K,
	const StrainField_t & delF,
	StressField_t & delP);
	/**
	* vectorized version for eigen solvers, no copy, but only works
	* when fields have ArrayStore=false
	*/
	Vector_ref directional_stiffness_vec(const Eigen::Ref<const Vector_t> & delF);
	/**
	* Evaluate directional stiffness into a temporary array and
	* return a copy. This is a costly and wasteful interface to
	* directional_stiffness and should only be used for debugging or
	* in the python interface
	*/
	Eigen::ArrayXXd directional_stiffness_with_copy
	(Eigen::Ref<Eigen::ArrayXXd> delF);

	/**
	* Convenience function circumventing the neeed to use the
	* underlying projection
	*/
	StressField_t & project(StressField_t & field);

	//! returns a ref to the cell's strain field
	StrainField_t & get_strain();

	//! returns a ref to the cell's stress field
	const StressField_t & get_stress() const;

	//! returns a ref to the cell's tangent stiffness field
	const TangentField_t & get_tangent(bool create = false);

	//! returns a ref to a temporary field managed by the cell
	StrainField_t & get_managed_field(std::string unique_name);

	/**
	* general initialisation; initialises the projection and
	* fft_engine (i.e. infrastructure) but not the materials. These
	* need to be initialised separately
	*/
	void initialise(FFT_PlanFlags flags = FFT_PlanFlags::estimate);

	/**
	* for materials with state variables, these typically need to be
	* saved/updated an the end of each load increment, this function
	* calls this update for each material in the cell
	*/
	void save_history_variables() override final;

	iterator begin(); //!< iterator to the first pixel
	iterator end(); //!< iterator past the last pixel
	//! number of pixels in the cell
	size_t size() const {return pixels.size();}

	//! return the subdomain resolutions of the cell
	const Ccoord & get_subdomain_resolutions() const {
	return this->subdomain_resolutions;}
	//! return the subdomain locations of the cell
	const Ccoord & get_subdomain_locations() const {
	return this->subdomain_locations;}
	//! return the domain resolutions of the cell
	const Ccoord & get_domain_resolutions() const {
	return this->domain_resolutions;}
	//! return the sizes of the cell
	const Rcoord & get_domain_lengths() const {return this->domain_lengths;}

	/**
	* formulation is hard set by the choice of the projection class
	*/
	const Formulation & get_formulation() const override final {
	return this->projection->get_formulation();}

	/**
	* get a reference to the projection object. should only be
	* required for debugging
	*/
	Eigen::Map<Eigen::ArrayXXd> get_projection() {
	return this->projection->get_operator();}

	//! returns the spatial size
	constexpr static Dim_t get_sdim() {return DimS;};

	//! return a sparse matrix adaptor to the cell
	Adaptor get_adaptor() override;
	//! returns the number of degrees of freedom in the cell
	Dim_t get_nb_dof() const override {return this->size()*ipow(DimS, 2);};

	//! return the communicator object
	virtual const Communicator & get_communicator() const override {
	return this->projection->get_communicator();
	}

	protected:
	//! make sure that every pixel is assigned to one and only one material
	void check_material_coverage();

	const Ccoord & subdomain_resolutions; //!< the cell's subdomain resolutions
	const Ccoord & subdomain_locations; //!< the cell's subdomain resolutions
	const Ccoord & domain_resolutions; //!< the cell's domain resolutions
	CcoordOps::Pixels<DimS> pixels; //!< helper to iterate over the pixels
	const Rcoord & domain_lengths; //!< the cell's lengths
	Collection_ptr fields; //!< handle for the global fields of the cell
	StrainField_t & F; //!< ref to strain field
	StressField_t & P; //!< ref to stress field
	//! Tangent field might not even be required; so this is an
	//! optional ref_wrapper instead of a ref
	optional<std::reference_wrapper<TangentField_t>> K{};
	//! container of the materials present in the cell
	std::vector<Material_ptr> materials{};
	Projection_ptr projection; //!< handle for the projection operator
	const Formulation form; //!< formulation for solution
	private:
	};


	/**
	* lightweight resource handle wrapping a `muSpectre::Cell` or
	* a subclass thereof into `Eigen::EigenBase`, so it can be
	* interpreted as a sparse matrix by Eigen solvers
	*/
	template <class Cell>
	class CellAdaptor: public Eigen::EigenBase<CellAdaptor<Cell>> {

	public:
	using Scalar = double; //!< sparse matrix traits
	using RealScalar = double; //!< sparse matrix traits
	using StorageIndex = int; //!< sparse matrix traits
	enum {
	ColsAtCompileTime = Eigen::Dynamic,
	MaxColsAtCompileTime = Eigen::Dynamic,
	RowsAtCompileTime = Eigen::Dynamic,
	MaxRowsAtCompileTime = Eigen::Dynamic,
	IsRowMajor = false
	};

	//! constructor
	CellAdaptor(Cell & cell):cell{cell}{}
	//!returns the number of logical rows
	Eigen::Index rows() const {return this->cell.get_nb_dof();}
	//!returns the number of logical columns
	Eigen::Index cols() const {return this->rows();}

	//! implementation of the evaluation
	template<typename Rhs>
	Eigen::Product<CellAdaptor,Rhs,Eigen::AliasFreeProduct>
	operator*(const Eigen::MatrixBase<Rhs>& x) const {
	return Eigen::Product<CellAdaptor,Rhs,Eigen::AliasFreeProduct>
	(*this, x.derived());
	}
	Cell & cell; //!< ref to the cell
	};

	} // muSpectre


	namespace Eigen {
	namespace internal {
	//! Implementation of `muSpectre::CellAdaptor` * `Eigen::DenseVector` through a
	//! specialization of `Eigen::internal::generic_product_impl`:
	template<typename Rhs, class CellAdaptor>
	struct generic_product_impl<CellAdaptor, Rhs, SparseShape, DenseShape, GemvProduct> // GEMV stands for matrix-vector
	: generic_product_impl_base<CellAdaptor,Rhs,generic_product_impl<CellAdaptor,Rhs> >
	{
	//! undocumented
	typedef typename Product<CellAdaptor,Rhs>::Scalar Scalar;

	//! undocumented
	template<typename Dest>
	static void scaleAndAddTo(Dest& dst, const CellAdaptor& lhs, const Rhs& rhs, const Scalar& /alpha/)
	{
	// This method should implement "dst += alpha * lhs * rhs" inplace,
	// however, for iterative solvers, alpha is always equal to 1, so let's not bother about it.
	// Here we could simply call dst.noalias() += lhs.my_matrix() * rhs,
	dst.noalias() += const_cast<CellAdaptor&>(lhs).cell.
	evaluate_projected_directional_stiffness(rhs);
	}
	};
	}
	}


	#endif /* CELL_BASE_H */

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