Sub_Matrix_Decomposition.cpp

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/*
Created on Fri Jun 26 14:13:26 2020
Copyright 2020 Peter Rakyta, Ph.D.

Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at

    http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.

@author: Peter Rakyta, Ph.D.
*/
#include "Sub_Matrix_Decomposition.h"
#include "Sub_Matrix_Decomposition_Cost_Function.h"

#include "BFGS_Powell.h"


#ifdef __MPI__
#include <mpi.h>
#endif // MPI

//tbb::spin_mutex my_mutex;

Sub_Matrix_Decomposition::Sub_Matrix_Decomposition( ) {

    // logical value. Set true if finding the minimum number of gate layers is required (default), or false when the maximal number of CNOT gates is used (ideal for general unitaries).
    optimize_layer_num  = false;

    // A string describing the type of the class
    type = SUB_MATRIX_DECOMPOSITION_CLASS;

    // The global minimum of the optimization problem
    global_target_minimum = 0;

    // logical value indicating whether the quasi-unitarization of the submatrices was done or not
    subdisentaglement_done = false;

    // custom gate structure used in the decomposition
    unit_gate_structure = NULL;

    max_inner_iterations = 100;

}


Sub_Matrix_Decomposition::Sub_Matrix_Decomposition( Matrix Umtx_in, int qbit_num_in, bool optimize_layer_num_in, std::map<std::string, Config_Element>& config_in, guess_type initial_guess_in= CLOSE_TO_ZERO ) : Decomposition_Base(Umtx_in, qbit_num_in, config_in, initial_guess_in) {

    // logical value. Set true if finding the minimum number of gate layers is required (default), or false when the maximal number of CNOT gates is used (ideal for general unitaries).
    optimize_layer_num  = optimize_layer_num_in;

    // A string describing the type of the class
    type = SUB_MATRIX_DECOMPOSITION_CLASS;

    // The global minimum of the optimization problem
    global_target_minimum = 0;

    // number of iteratrion loops in the optimization
    iteration_loops[2] = 3;

    // logical value indicating whether the quasi-unitarization of the submatrices was done or not
    subdisentaglement_done = false;

    // filling in numbers that were not given in the input
    for ( std::map<int,int>::iterator it = max_layer_num_def.begin(); it!=max_layer_num_def.end(); it++) {
        if ( max_layer_num.count( it->first ) == 0 ) {
            max_layer_num.insert( std::pair<int, int>(it->first,  it->second) );
        }
    }

    // custom gate structure used in the decomposition
    unit_gate_structure = NULL;

    max_inner_iterations = 100;


}


Sub_Matrix_Decomposition::~Sub_Matrix_Decomposition() {

    if ( unit_gate_structure != NULL ) {
        delete unit_gate_structure;
    }
    unit_gate_structure = NULL;

}






void  Sub_Matrix_Decomposition::disentangle_submatrices() {

    if (subdisentaglement_done) {        
     std::stringstream sstream;
     sstream << "Sub-disentaglement already done." << std::endl;
     print(sstream, 2);       
        return;
    }   

    std::stringstream sstream;
    sstream << std::endl << "Disentagling submatrices." << std::endl;
    print(sstream, 2);        
      
    
    // setting the global target minimum
    global_target_minimum = 0;
    current_minimum = optimization_problem(NULL);

    // check if it needed to do the subunitarization
    if (check_optimization_solution()) {
        std::stringstream sstream;
        sstream << "Disentanglig not needed" << std::endl;
        print(sstream, 2);                             
        subdecomposed_mtx = Umtx;
        subdisentaglement_done = true;
        return;
    }


    if ( !check_optimization_solution() ) {
        // Adding the gates of the successive layers

        //measure the time for the decompositin
        tbb::tick_count start_time = tbb::tick_count::now();

        // the maximal number of layers in the subdeconposition
        int max_layer_num_loc;
        try {
            max_layer_num_loc = max_layer_num[qbit_num];
        }
        catch (...) {
            std::stringstream sstream;
         sstream << "Layer number not given" << std::endl;
         print(sstream, 0);       
            throw sstream.str();
        }

        while ( layer_num < max_layer_num_loc ) {

            // add another gate layers to the gate structure used in the decomposition
            add_gate_layers();

            // get the number of blocks
            layer_num = gates.size();

            // Do the optimization
            if (optimize_layer_num || layer_num >= max_layer_num_loc ) {

                // solve the optimization problem to find the correct minimum
                solve_optimization_problem( NULL, 0);

                if (check_optimization_solution()) {
                    break;
                }
            }

        }

        
        tbb::tick_count current_time = tbb::tick_count::now();

     std::stringstream sstream;
     sstream << "--- " << (current_time - start_time).seconds() << " seconds elapsed during the decomposition ---" << std::endl << std::endl;
     print(sstream, 2);       
     
    }



    if (check_optimization_solution()) {
       std::stringstream sstream;
       sstream << "Sub-disentaglement was succesfull." << std::endl << std::endl;
       print(sstream, 1);              
    }
    else {
       std::stringstream sstream;
       sstream << "Sub-disentaglement did not reach the tolerance limit." << std::endl << std::endl;
       print(sstream, 1);          
    }


    // indicate that the unitarization of the sumbatrices was done
    subdisentaglement_done = true;

    // The subunitarized matrix
    subdecomposed_mtx = Umtx.copy();
    apply_to( optimized_parameters_mtx, subdecomposed_mtx );

}

void Sub_Matrix_Decomposition::add_gate_layers() {

    if ( unit_gate_structure == NULL ) {
        // add default gate structure if custom is not given
        add_default_gate_layers();
        return;
    }

    // add custom gate structure

    // the  number of succeeding identical layers in the subdecomposition
    int identical_blocks_loc;
    try {
        identical_blocks_loc = identical_blocks[qbit_num];
        if (identical_blocks_loc==0) {
            identical_blocks_loc = 1;
        }
    }
    catch (...) {
        identical_blocks_loc=1;
    }

    // get the list of sub-blocks in the custom gate structure
    std::vector<Gate*> gates = unit_gate_structure->get_gates();

    for (std::vector<Gate*>::iterator gates_it = gates.begin(); gates_it != gates.end(); gates_it++ ) {

        // The current gate
        Gate* gate = *gates_it;

        for (int idx=0;  idx<identical_blocks_loc; idx++) {
            add_gate( (Gate*)(gate->clone()) );
        }
        
    }


}



void Sub_Matrix_Decomposition::add_default_gate_layers() {

    int control_qbit_loc = qbit_num-1;

    // the  number of succeeding identical layers in the subdecomposition
    int identical_blocks_loc;
    try {
        identical_blocks_loc = identical_blocks[qbit_num];
        if (identical_blocks_loc==0) {
            identical_blocks_loc = 1;
        }
    }
    catch (...) {
        identical_blocks_loc=1;
    }


    for (int target_qbit_loc = 0; target_qbit_loc<control_qbit_loc; target_qbit_loc++ ) {

        for (int idx=0;  idx<identical_blocks_loc; idx++) {

            // creating block of gates
            Gates_block* block = new Gates_block( qbit_num );

            // adding U3 gate to the block
            block->add_u3(target_qbit_loc);
            block->add_u3(control_qbit_loc);


            // add CNOT gate to the block
            block->add_cnot(target_qbit_loc, control_qbit_loc);

            // adding the opeartion block to the gates
            add_gate( block );

        }
    }


}



void Sub_Matrix_Decomposition::set_custom_gate_layers( Gates_block* block_in) {

    unit_gate_structure = block_in->clone();

}





void Sub_Matrix_Decomposition::solve_layer_optimization_problem( int num_of_parameters, Matrix_real solution_guess) {


        if (gates.size() == 0 ) {
            return;
        }


        if (solution_guess.size() == 0 ) {
            solution_guess = Matrix_real(num_of_parameters,1);
        }


        if (optimized_parameters_mtx.size() == 0) {
            optimized_parameters_mtx = Matrix_real(1, num_of_parameters);
            memcpy(optimized_parameters_mtx.get_data(), solution_guess.get_data(), num_of_parameters*sizeof(double) );
        }


        // maximal number of iteration loops
        int iteration_loops_max;
        try {
            iteration_loops_max = std::max(iteration_loops[qbit_num], 1);
        }
        catch (...) {
            iteration_loops_max = 1;
        }

        // maximal number of inner iterations overriden by config
        long long max_inner_iterations_loc;
        if ( config.count("max_inner_iterations") > 0 ) {
            config["max_inner_iterations"].get_property( max_inner_iterations_loc );         
        }
        else {
            max_inner_iterations_loc =max_inner_iterations;
        }

        // random generator of real numbers   
        std::uniform_real_distribution<> distrib_real(0.0, 2*M_PI);

        // do the optimization loops
        for (long long idx=0; idx<iteration_loops_max; idx++) {

            BFGS_Powell cBFGS_Powell(optimization_problem_combined, this);
            double f = cBFGS_Powell.Start_Optimization(solution_guess, max_inner_iterations);


            if (current_minimum > f) {
                current_minimum = f;
                memcpy( optimized_parameters_mtx.get_data(), solution_guess.get_data(), num_of_parameters*sizeof(double) );
                for ( int jdx=0; jdx<num_of_parameters; jdx++) {
                    solution_guess[jdx] = solution_guess[jdx] + distrib_real(gen)/100;
                }
            }
            else {
                for ( int jdx=0; jdx<num_of_parameters; jdx++) {
                    solution_guess[jdx] = solution_guess[jdx] + distrib_real(gen);
                }
            }

#ifdef __MPI__        
            MPI_Bcast( (void*)solution_guess.get_data(), num_of_parameters, MPI_DOUBLE, 0, MPI_COMM_WORLD);
#endif



        }


}




double Sub_Matrix_Decomposition::optimization_problem( double* parameters ) {

        // get the transformed matrix with the gates in the list
        Matrix_real parameters_mtx(parameters, 1, parameter_num );
        Matrix matrix_new = Umtx.copy();
        apply_to( parameters_mtx, matrix_new );

#ifdef DEBUG
        if (matrix_new.isnan()) {
           std::stringstream sstream;
        sstream << "Sub_Matrix_Decomposition::optimization_problem: matrix_new contains NaN a. Exiting" << std::endl;
        print(sstream, 1);    
        }
#endif

        double cost_function = get_submatrix_cost_function(matrix_new);


        return cost_function;
}


double Sub_Matrix_Decomposition::optimization_problem( Matrix_real parameters, void* void_instance ) {

    Sub_Matrix_Decomposition* instance = reinterpret_cast<Sub_Matrix_Decomposition*>(void_instance);
    std::vector<Gate*> gates_loc = instance->get_gates();

    Matrix Umtx_loc, matrix_new;

//{
//tbb::spin_mutex::scoped_lock my_lock{my_mutex};

    Umtx_loc = instance->get_Umtx();
    matrix_new = Umtx_loc.copy();
    instance->apply_to( parameters, matrix_new );

#ifdef DEBUG
        if (matrix_new.isnan()) {
           std::stringstream sstream;
        sstream << "Sub_Matrix_Decomposition::optimization_problem matrix_new contains NaN b." << std::endl;
        print(sstream, 1);     
        }
#endif

//}


    double cost_function = get_submatrix_cost_function(matrix_new);  //NEW METHOD


    return cost_function;
}





void Sub_Matrix_Decomposition::optimization_problem_grad( Matrix_real parameters, void* void_instance, Matrix_real& grad ) {

    // The function value at x0
    double f0;

    // calculate the approximate gradient
    optimization_problem_combined( parameters, void_instance, &f0, grad);

}



void Sub_Matrix_Decomposition::optimization_problem_combined( Matrix_real parameters, void* void_instance, double* f0, Matrix_real& grad ) {

    Sub_Matrix_Decomposition* instance = reinterpret_cast<Sub_Matrix_Decomposition*>(void_instance);

    int parameter_num_loc = instance->get_parameter_num();

    // storage for the function values calculated at the displaced points x
    Matrix_real f(1, grad.size());

    // the difference in one direction in the parameter for the gradient calculation
    double dparam = 1e-8;

    // calculate the function values at displaced x and the central x0 points through TBB parallel for
    tbb::parallel_for(0, parameter_num_loc+1, 1, [&](int i) {

        if (i == (int)parameters.size()) {
            // calculate function value at x0
            *f0 = instance->optimization_problem(parameters, reinterpret_cast<void*>(instance));
        }
        else {

            Matrix_real parameters_d = parameters.copy();
            parameters_d[i] = parameters_d[i] + dparam;

            // calculate the cost function at the displaced point
            f[i] = instance->optimization_problem(parameters_d, reinterpret_cast<void*>(instance));

        }
    });


/*
    // sequential version
    functor_sub_optimization_grad<Sub_Matrix_Decomposition> tmp = functor_grad<Sub_Matrix_Decomposition>( parameters, instance, f, f0, dparam );
    #pragma omp parallel for
    for (int idx=0; idx<parameter_num_loc+1; idx++) {
        tmp(idx);
    }
*/


    for (int idx=0; idx<parameter_num_loc; idx++) {
        // set the gradient
#ifdef DEBUG
        if (isnan(f->data[idx])) {
          std::string err("Sub_Matrix_Decomposition::optimization_problem_combined: f->data[i] is NaN.");
          throw err;
        }
#endif // DEBUG
        grad[idx] = (f[idx]-(*f0))/dparam;
    }



}










int Sub_Matrix_Decomposition::set_identical_blocks( int qbit, int identical_blocks_in )  {

    std::map<int,int>::iterator key_it = identical_blocks.find( qbit );

    if ( key_it != identical_blocks.end() ) {
        identical_blocks.erase( key_it );
    }

    identical_blocks.insert( std::pair<int, int>(qbit,  identical_blocks_in) );

    return 0;

}


int Sub_Matrix_Decomposition::set_identical_blocks( std::map<int, int> identical_blocks_in )  {

    for ( std::map<int,int>::iterator it=identical_blocks_in.begin(); it!= identical_blocks_in.end(); it++ ) {
        set_identical_blocks( it->first, it->second );
    }

    return 0;

}


Sub_Matrix_Decomposition* Sub_Matrix_Decomposition::clone() {


    Sub_Matrix_Decomposition* ret = new Sub_Matrix_Decomposition(Umtx, qbit_num, optimize_layer_num, config, initial_guess);

    // setting computational parameters
    ret->set_identical_blocks( identical_blocks );
    ret->set_max_iteration( max_outer_iterations );
    ret->set_optimization_blocks( optimization_block );
    ret->set_max_layer_num( max_layer_num );
    ret->set_iteration_loops( iteration_loops );

    if ( extract_gates(static_cast<Gates_block*>(ret)) != 0 ) {
        std::string err("Sub_Matrix_Decomposition::clone(): extracting gates was not succesfull.");
        throw err;
    }

    return ret;

}