/* linbox/algorithms/la-block-lanczos.h
 * Copyright 2002-2004 Bradford Hovinen
 *
 * Written by Bradford Hovinen <bghovinen@math.waterloo.ca>
 *
 * --------------------------------------------
 *
 * details.
 * ========LICENCE========
 * This file is part of the library LinBox.
 *
 * LinBox is free software: you can 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.
 *
 * This library 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
 * Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public
 * License along with this library; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301  USA
 * ========LICENCE========

 * Class definitions for block Lanczos iteration
 */

#ifndef __LINBOX_la_block_lanczos_H
#define __LINBOX_la_block_lanczos_H

#include "linbox/linbox-config.h"

#include <vector>
#include <deque>

#include "linbox/field/archetype.h"
#include "linbox/vector/vector-domain.h"
#include "linbox/blackbox/archetype.h"
#include "linbox/solutions/methods.h"
#include "linbox/algorithms/eliminator.h"

namespace LinBox
{

	/** Biorthogonalising block Lanczos iteration
	 *
	 * This is a biorthogonalising variant of Montgomery's block Lanczos
	 * iteration. The goal is to avoid having to symmetrise the input
	 * matrix by constructing two sequences of block vectors that have
	 * mutual orthogonality properties. This algorithm was proposed by
	 * Bradford Hovinen.
	 */
	template <class Field, class Matrix = BlasMatrix<typename Field::Element> >
	class LABlockLanczosSolver {
	public:

		typedef typename Field::Element Element;

		/** Constructor
		 * @param F Field over which to operate
		 * @param traits @ref SolverTraits structure describing user
		 *               options for the solver
		 */
		LABlockLanczosSolver (const Field &F,
				      const BlockLanczosTraits &traits) :
			_traits (traits), _field (F), _VD (F), _MD (F), _randiter (F),
			_uAv (this), _eliminator (F, _traits.blockingFactor ())
		{ init_temps (); }

		/** Constructor with a random iterator
		 * @param F Field over which to operate
		 * @param traits @ref SolverTraits structure describing user
		 *               options for the solver
		 * @param r Random iterator to use for randomization
		 */
		LABlockLanczosSolver (const Field &F,
				      const BlockLanczosTraits &traits,
				      typename Field::RandIter r) :
			_traits (traits), _field (F), _VD (F), _MD (F), _randiter (r),
			_uAv (this),
			_eliminator (F, (unsigned int)  _traits.blockingFactor ())
		{ init_temps (); }

		/** Destructor
		*/
		~LABlockLanczosSolver ();

		/** Solve the linear system Ax = b.
		 *
		 * If the system is nonsingular, this method computes the unique
		 * solution to the system Ax = b. If the system is singular, it computes
		 * a random solution.
		 *
		 * @param A Black box for the matrix A
		 * @param x Vector in which to store solution
		 * @param b Right-hand side of system
		 * @return True on success; false on failure
		 */
		template <class Blackbox, class Vector>
		bool solve (const Blackbox &A, Vector &x, const Vector &b);

		/** Sample uniformly from the (right) nullspace of A
		 *
		 * @param A Black box for the matrix A
		 * @param x Matrix into whose columns to store nullspace elements
		 * @return Number of nullspace vectors found
		 */
		template <class Blackbox, class Matrix1>
		unsigned int sampleNullspace (const Blackbox &A, Matrix1 &x);

		/** Estimate the rank of A
		 *
		 * @param A Black box for the matrix A
		 * @return Lower bound on the rank of A
		 */
		template <class Blackbox>
		unsigned int rank (const Blackbox &A);

	private:

		typedef typename MatrixDomain<Field>::Permutation Permutation;

		class BasisTransformation {
			LABlockLanczosSolver      &_solver;

			std::vector<Permutation>   _permP;
			std::vector<Matrix *>      _multiMat;
			std::vector<unsigned int>  _rho;
			std::vector<unsigned int>  _s;

			unsigned int _number;

			template <class Matrix1>
			void applyOne (Matrix1 &M, Permutation &P, Matrix *T, unsigned int rho, unsigned int s, bool left);

		public:
			template <class Matrix1>
			Matrix1 &apply (Matrix1 &A, bool left);

			template <class Matrix1>
			Matrix1 &applyPermutation (Matrix1 &A, bool left);

			template <class Matrix1>
			Matrix1 &applyLast (Matrix1 &A, bool left);

			template <class Matrix1>
			void append (Permutation &P, Matrix1 &T, unsigned int rho);

			void reset ();

			void reportComplete (std::ostream &out);
			void report (std::ostream &out);

			BasisTransformation (LABlockLanczosSolver<Field, Matrix> &solver, unsigned int N) :
				_solver (solver), _number (N)
			{ reset (); }

			~BasisTransformation ();
		};

		friend class BasisTransformation;

		struct Iterate;

		// Structure representing an elimination step
		struct ElimStep
		{
			Matrix *_ujAvkmu;
			Matrix *_nuukAvj;

			unsigned int _rho;
			unsigned int _rhop;

			Iterate *_l;
			int _l_iter;
		};

		// Structure representing an iterate
		struct Iterate
		{
			// Record of the pseudoinverse
			Matrix _udotAvbarinv;       // N x N
			Matrix _ubarAvdotinv;       // N x N

			// Record of the iterate from this iteration
			Matrix _u;                  // N x n
			Matrix _v;                  // N x n

			// Record of the dot iterate from this iteration
			Matrix _udot;               // N x n
			Matrix _vdot;               // N x n

			// Record of the basis transformation
			BasisTransformation _sigma_u;
			BasisTransformation _sigma_v;

			// Record of udot_j^TAv_j and u_j^TAvdot_j
			Matrix _udotAv;             // N x N
			Matrix _uAvdot;             // N x N

			// Record of elimination steps used on _u and _v
			std::list<ElimStep> _steps;

			int _iter;
			unsigned int _rho_u, _rho_v;
			bool _done;

			Iterate (LABlockLanczosSolver &solver, size_t n, size_t N, unsigned int iter) :
				_udotAvbarinv (N, N), _ubarAvdotinv (N, N),
				_u (n, N), _v (n, N), _udot (n, N), _vdot (n, N),
				_sigma_u (solver,  (unsigned int) N),
			       	_sigma_v (solver,  (unsigned int) N),
				_udotAv (N, N), _uAvdot (N, N)
			{ init (iter); }

			void init (unsigned int iter)
			{
				_iter = iter;
				_rho_u = _rho_v = 0;
				_done = false;
				_sigma_u.reset ();
				_sigma_v.reset ();
				_steps.clear ();
			}
		};

		// Two-dimensional array of inner products

		class InnerProductArray {
			LABlockLanczosSolver *_solver;
			std::deque<std::deque<Matrix *> > _blocks;
			unsigned int _base;

		public:
			InnerProductArray (LABlockLanczosSolver *solver) :
				_solver (solver), _base (0)
			{}

			void extend ();
			void contract ();
			Matrix *get (int i, int j);
			void reset ();
		};

		// Run the block Lanczos iteration and return the result. Return false
		// if the method breaks down. Do not check that Ax = b in the end
		template <class Blackbox>
		void iterate (const Blackbox &A);

		template <class Matrix1>
		void fixInnerProducts (typename std::list<Iterate *>::iterator l, const Matrix1 &Cu, const Matrix1 &Cv, unsigned int iter);

		template <class Blackbox>
		void tailDecomp (typename std::list<Iterate *>::iterator l, Iterate *i, const Blackbox &A);

		// Clean up the queue of iterates and return an Iterate structure to
		// store the next iterate information
		void cleanup (bool all);

		void adjust_uip1Abeta (typename std::list<Iterate *>::iterator j,
				       ElimStep &step,
				       unsigned int iter);
		void compute_uip1Abeta (typename std::list<Iterate *>::iterator j, unsigned int iter);
		void adjust_alphaAvip1 (typename std::list<Iterate *>::iterator j,
					ElimStep &step,
					unsigned int iter);
		void compute_alphaAvip1 (typename std::list<Iterate *>::iterator j, unsigned int iter);

		void augmentuidotAv (Iterate *i, Iterate *l, unsigned int rho);
		void augmentuAvidot (Iterate *i, Iterate *l, unsigned int rho);

		// Augment the inner products in udotAv with information on a new profile
		void augmentuldotAv (Iterate *l, Iterate *i, std::vector<unsigned int> &profile, unsigned int rho);

		// Augment the inner products in uAvdot with information on a new profile
		void augmentuAvldot (Iterate *l, Iterate *i, std::vector<unsigned int> &profile, unsigned int rho);

		template <class Matrix1, class Matrix2>
		void extractMinor (Matrix1 &M, Matrix2 &M1, std::vector<unsigned int> &profile);

		// Retrieve a new iterate structure
		Iterate *getNextIterate (unsigned int iter);

		// Management of the grid of inner products
		Matrix *newBlock ();

		// Initialize the temporaries used in computation
		void init_temps ();

		template <class Blackbox>
		void checkInnerProducts (const Blackbox &A);

		template <class Matrix1, class Matrix2, class Blackbox>
		void checkAConjugacy (const Matrix1  &u,
				      const Matrix2  &v,
				      const Blackbox &A,
				      size_t          u_iter,
				      size_t          v_iter,
				      size_t          rho_u,
				      size_t          rho_v);

		template <class T>
		inline const T &max (const T &a, const T &b) const
		{
			return (a > b) ? a : b;
		}

		template <class T>
		inline const T &min (const T &a, const T &b) const
		{
			return (a < b) ? a : b;
		}

		// Private variables

		const BlockLanczosTraits  _traits;
		const Field               &_field;
		VectorDomain<Field>        _VD;
		MatrixDomain<Field>        _MD;
		typename Field::RandIter   _randiter;

		// Temporaries used in the computation

		mutable Matrix    _T1;           // N x N
		mutable Matrix    _T2;           // N x N
		mutable Matrix    _T3;           // N x N
		mutable Matrix    _T4;           // N x N
		mutable Matrix    _T5;           // N x N
		mutable Matrix    _matW;            // N x N

		Matrix            _ATu;          // n x N
		Matrix            _Av;           // n x N

		Matrix            _Cu;           // N x N
		Matrix            _Cv;           // N x N

		Permutation       _permP;
		Permutation       _permQ;

		Matrix            _v0;           // n x N
		Matrix            _b;            // n x <=N
		Matrix            _x;            // n x <=N
		Matrix            _y;            // n x <=N

		Element           _one;

		unsigned int	  _iter;
		unsigned int	  _total_dim;
		unsigned int	  _rank;

		std::vector<unsigned int> _profile;

		// Records used in managing Ucirc and Vcirc
		std::map<unsigned int, unsigned int> _gamma;

		InnerProductArray _uAv;  // Array of inner products wrt. original bases

		std::list<Iterate *>  _history;
		std::stack<Iterate *> _it_trashcan; // Unused Iterate structures go here
		std::stack<Matrix *>  _ip_trashcan; // Unused inner product matrices
		// go here

		Eliminator<Field, Matrix> _eliminator;

		// Construct a transpose matrix on the fly
		template <class Matrix1>
		static inline TransposeMatrix<Matrix1> transpose (Matrix1 &M)
		{ return TransposeMatrix<Matrix1> (M); }
	};

} // namespace LinBox

#include "linbox/algorithms/la-block-lanczos.inl"

#endif // __LINBOX_la_block_lanczos_H


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