Program Listing for File state_dm.hpp

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#pragma once

#include <csim/memory_ops_dm.hpp>
#include <csim/stat_ops_dm.hpp>
#include <csim/update_ops_dm.hpp>

#include "state.hpp"

class DensityMatrixCpu : public QuantumStateBase {
private:
    CPPCTYPE* _density_matrix;
    Random random;

public:
    explicit DensityMatrixCpu(UINT qubit_count_)
        : QuantumStateBase(qubit_count_, false) {
        this->_density_matrix =
            reinterpret_cast<CPPCTYPE*>(dm_allocate_quantum_state(this->_dim));
        dm_initialize_quantum_state(this->data_c(), _dim);
    }
    virtual ~DensityMatrixCpu() { dm_release_quantum_state(this->data_c()); }
    virtual void set_zero_state() override {
        dm_initialize_quantum_state(this->data_c(), _dim);
    }

    virtual void set_zero_norm_state() override {
        set_zero_state();
        _density_matrix[0] = 0.;
    }

    virtual void set_computational_basis(ITYPE comp_basis) override {
        if (comp_basis >= (ITYPE)(1ULL << this->qubit_count)) {
            throw MatrixIndexOutOfRangeException(
                "Error: DensityMatrixCpu::set_computational_basis(ITYPE): "
                "index "
                "of computational basis must be smaller than 2^qubit_count");
        }
        set_zero_state();
        _density_matrix[0] = 0.;
        _density_matrix[comp_basis * dim + comp_basis] = 1.;
    }
    virtual void set_Haar_random_state() override {
        this->set_Haar_random_state(random.int32());
    }
    virtual void set_Haar_random_state(UINT seed) override {
        QuantumStateCpu* pure_state = new QuantumStateCpu(qubit_count);
        pure_state->set_Haar_random_state(seed);
        dm_initialize_with_pure_state(
            this->data_c(), pure_state->data_c(), _dim);
        delete pure_state;
    }
    virtual double get_zero_probability(
        UINT target_qubit_index) const override {
        if (target_qubit_index >= this->qubit_count) {
            throw QubitIndexOutOfRangeException(
                "Error: DensityMatrixCpu::get_zero_probability(UINT): index "
                "of target qubit must be smaller than qubit_count");
        }
        return dm_M0_prob(target_qubit_index, this->data_c(), _dim);
    }
    virtual double get_marginal_probability(
        std::vector<UINT> measured_values) const override {
        if (measured_values.size() != this->qubit_count) {
            throw InvalidQubitCountException(
                "Error: "
                "DensityMatrixCpu::get_marginal_probability(vector<UINT>): "
                "the length of measured_values must be equal to qubit_count");
        }

        std::vector<UINT> target_index;
        std::vector<UINT> target_value;
        for (UINT i = 0; i < measured_values.size(); ++i) {
            UINT measured_value = measured_values[i];
            if (measured_value == 0 || measured_value == 1) {
                target_index.push_back(i);
                target_value.push_back(measured_value);
            }
        }
        return dm_marginal_prob(target_index.data(), target_value.data(),
            (UINT)target_index.size(), this->data_c(), _dim);
    }

    virtual double get_entropy() const override {
        return dm_measurement_distribution_entropy(this->data_c(), _dim);
    }

    virtual double get_squared_norm() const override {
        return dm_state_norm_squared(this->data_c(), _dim);
    }

    virtual double get_squared_norm_single_thread() const override {
        return dm_state_norm_squared(this->data_c(), _dim);
    }

    virtual void normalize(double squared_norm) override {
        dm_normalize(squared_norm, this->data_c(), _dim);
    }

    virtual void normalize_single_thread(double squared_norm) override {
        dm_normalize(squared_norm, this->data_c(), _dim);
    }

    virtual DensityMatrixCpu* allocate_buffer() const override {
        DensityMatrixCpu* new_state = new DensityMatrixCpu(this->_qubit_count);
        return new_state;
    }
    virtual DensityMatrixCpu* copy() const override {
        DensityMatrixCpu* new_state = new DensityMatrixCpu(this->_qubit_count);
        memcpy(new_state->data_cpp(), _density_matrix,
            (size_t)(sizeof(CPPCTYPE) * _dim * _dim));
        for (UINT i = 0; i < _classical_register.size(); ++i)
            new_state->set_classical_value(i, _classical_register[i]);
        return new_state;
    }
    virtual void load(const QuantumStateBase* _state) override {
        if (_state->qubit_count != this->qubit_count) {
            throw InvalidQubitCountException(
                "Error: DensityMatrixCpu::load(const QuantumStateBase*): "
                "invalid qubit count");
        }
        if (_state->outer_qc > 0) {
            throw NotImplementedException(
                "Error: DensityMatrixCpu::load(const QuantumStateBase*) "
                "using multi-cpu is not implemented");
        }
        if (_state->is_state_vector()) {
            if (_state->get_device_name() == "gpu") {
                auto ptr = _state->duplicate_data_c();
                dm_initialize_with_pure_state(this->data_c(), ptr, dim);
                free(ptr);
            } else {
                dm_initialize_with_pure_state(
                    this->data_c(), _state->data_c(), dim);
            }
        } else {
            memcpy(this->data_cpp(), _state->data_cpp(),
                (size_t)(sizeof(CPPCTYPE) * _dim * _dim));
        }
        this->_classical_register = _state->classical_register;
    }
    virtual void load(const std::vector<CPPCTYPE>& _state) override {
        if (_state.size() != _dim && _state.size() != _dim * _dim) {
            throw InvalidStateVectorSizeException(
                "Error: DensityMatrixCpu::load(vector<Complex>&): invalid "
                "length of state");
        }
        if (_state.size() == _dim) {
            dm_initialize_with_pure_state(
                this->data_c(), (const CTYPE*)_state.data(), dim);
        } else {
            memcpy(this->data_cpp(), _state.data(),
                (size_t)(sizeof(CPPCTYPE) * _dim * _dim));
        }
    }

    virtual void load(const Eigen::VectorXcd& _state) {
        ITYPE arg_dim = _state.size();
        if (arg_dim != _dim && arg_dim != _dim * _dim) {
            throw InvalidStateVectorSizeException(
                "Error: DensityMatrixCpu::load(vector<Complex>&): invalid "
                "length of state");
        }
        if (arg_dim == _dim) {
            dm_initialize_with_pure_state(
                this->data_c(), (const CTYPE*)_state.data(), dim);
        } else {
            memcpy(this->data_cpp(), _state.data(),
                (size_t)(sizeof(CPPCTYPE) * _dim * _dim));
        }
    }

    virtual void load(const ComplexMatrix& _state) {
        ITYPE arg_cols = _state.cols();
        ITYPE arg_rows = _state.rows();
        if (arg_cols != _dim && arg_rows != _dim * _dim) {
            throw InvalidStateVectorSizeException(
                "Error: DensityMatrixCpu::load(ComplexMatrix&): invalid "
                "length of state");
        }
        memcpy(this->data_cpp(), _state.data(),
            (size_t)(sizeof(CPPCTYPE) * _dim * _dim));
    }

    virtual void load(const CPPCTYPE* _state) override {
        memcpy(
            this->data_cpp(), _state, (size_t)(sizeof(CPPCTYPE) * _dim * _dim));
    }

    virtual const std::string get_device_name() const override { return "cpu"; }

    virtual void* data() const override {
        return reinterpret_cast<void*>(this->_density_matrix);
    }
    virtual CPPCTYPE* data_cpp() const override {
        return this->_density_matrix;
    }
    virtual CTYPE* data_c() const override {
        return reinterpret_cast<CTYPE*>(this->_density_matrix);
    }

    virtual CTYPE* duplicate_data_c() const override {
        CTYPE* new_data = (CTYPE*)malloc(sizeof(CTYPE) * _dim * _dim);
        memcpy(new_data, this->data(), (size_t)(sizeof(CTYPE) * _dim * _dim));
        return new_data;
    }

    virtual CPPCTYPE* duplicate_data_cpp() const override {
        CPPCTYPE* new_data = (CPPCTYPE*)malloc(sizeof(CPPCTYPE) * _dim * _dim);
        memcpy(
            new_data, this->data(), (size_t)(sizeof(CPPCTYPE) * _dim * _dim));
        return new_data;
    }

    virtual void add_state(const QuantumStateBase* state) override {
        if (state->is_state_vector()) {
            throw NotImplementedException(
                "add state between density matrix and state vector is not "
                "implemented");
        }
        dm_state_add(state->data_c(), this->data_c(), this->dim);
    }

    virtual void add_state_with_coef(
        CPPCTYPE coef, const QuantumStateBase* state) override {
        if (state->is_state_vector()) {
            throw NotImplementedException(
                "add state between density matrix and state vector is not "
                "implemented");
        }
        dm_state_add_with_coef(
            coef, state->data_c(), this->data_c(), this->dim);
    }

    virtual void add_state_with_coef_single_thread(
        CPPCTYPE coef, const QuantumStateBase* state) override {
        if (state->is_state_vector()) {
            throw NotImplementedException(
                "add state between density matrix and state vector is not "
                "implemented");
        }
        dm_state_add_with_coef(
            coef, state->data_c(), this->data_c(), this->dim);
    }

    virtual void multiply_coef(CPPCTYPE coef) override {
        dm_state_multiply(coef, this->data_c(), this->dim);
    }

    virtual void multiply_elementwise_function(
        const std::function<CPPCTYPE(ITYPE)>&) override {
        throw NotImplementedException(
            "multiply_elementwise_function for density matrix is not "
            "implemented");
    }

    virtual std::vector<ITYPE> sampling(UINT sampling_count) override {
        std::vector<double> stacked_prob;
        std::vector<ITYPE> result;
        double sum = 0.;
        auto ptr = this->data_cpp();
        stacked_prob.push_back(0.);
        for (UINT i = 0; i < this->dim; ++i) {
            sum += abs(ptr[i * dim + i]);
            stacked_prob.push_back(sum);
        }

        for (UINT count = 0; count < sampling_count; ++count) {
            double r = random.uniform();
            auto ite =
                std::lower_bound(stacked_prob.begin(), stacked_prob.end(), r);
            auto index = std::distance(stacked_prob.begin(), ite) - 1;
            result.push_back(index);
        }
        return result;
    }

    virtual std::vector<ITYPE> sampling(
        UINT sampling_count, UINT random_seed) override {
        random.set_seed(random_seed);
        return this->sampling(sampling_count);
    }
    virtual std::string to_string() const override {
        std::stringstream os;
        ComplexMatrix eigen_state(this->dim, this->dim);
        auto data = this->data_cpp();
        for (UINT i = 0; i < this->dim; ++i) {
            for (UINT j = 0; j < this->dim; ++j) {
                eigen_state(i, j) = data[i * dim + j];
            }
        }
        os << " *** Density Matrix ***" << std::endl;
        os << " * Qubit Count : " << this->qubit_count << std::endl;
        os << " * Dimension   : " << this->dim << std::endl;
        os << " * Density matrix : \n" << eigen_state << std::endl;
        return os.str();
    }
    virtual boost::property_tree::ptree to_ptree() const override {
        boost::property_tree::ptree pt;
        pt.put("name", "DensityMatrix");
        pt.put("qubit_count", _qubit_count);
        pt.put_child(
            "classical_register", ptree::to_ptree(_classical_register));
        pt.put_child("density_matrix",
            ptree::to_ptree(std::vector<CPPCTYPE>(
                _density_matrix, _density_matrix + _dim * _dim)));
        return pt;
    }
};

using DensityMatrix = DensityMatrixCpu;

namespace state {
DllExport DensityMatrixCpu* tensor_product(
    const DensityMatrixCpu* state_bra, const DensityMatrixCpu* state_ket);
DllExport DensityMatrixCpu* permutate_qubit(
    const DensityMatrixCpu* state, std::vector<UINT> qubit_order);
DllExport DensityMatrixCpu* partial_trace(
    const QuantumStateCpu* state, std::vector<UINT> target);
DllExport DensityMatrixCpu* partial_trace(
    const DensityMatrixCpu* state, std::vector<UINT> target_traceout);
// create a mixed state such that the proportion of state1 is prob1, the
// proportion of state2 is prob2
DllExport DensityMatrixCpu* make_mixture(CPPCTYPE prob1,
    const QuantumStateBase* state1, CPPCTYPE prob2,
    const QuantumStateBase* state2);
DllExport QuantumStateBase* from_ptree(const boost::property_tree::ptree& pt);
}  // namespace state