GpuState.h

Go to the documentation of this file.

 
#pragma once
 
#ifndef _GPUSTATE_H_
#define _GPUSTATE_H_
 
#ifdef __linux__
 
#ifdef INCLUDED_BY_FACTORY
 
namespace Simulators {
// TODO: Maybe use the pimpl idiom
// https://en.cppreference.com/w/cpp/language/pimpl to hide the implementation
// for good but during development this should be good enough
namespace Private {

class GpuState : public ISimulator {
public:
  void Initialize() override {
    if (nrQubits) {
      if (simulationType == SimulationType::kStatevector) {
        state = SimulatorsFactory::CreateGpuLibStateVectorSim();
        if (state) {
          const bool res = state->Create(nrQubits);
          if (!res)
            throw std::runtime_error("GpuState::Initialize: Failed to create "
                                     "and initialize the statevector state.");
        } else
          throw std::runtime_error(
              "GpuState::Initialize: Failed to create the statevector state.");
      } else if (simulationType == SimulationType::kMatrixProductState) {
        mps = SimulatorsFactory::CreateGpuLibMPSSim();
        if (mps) {
          if (limitEntanglement && singularValueThreshold > 0.)
            mps->SetCutoff(singularValueThreshold);
          if (limitSize && chi > 0)
            mps->SetMaxExtent(chi);
          const bool res = mps->Create(nrQubits);
          if (!res)
            throw std::runtime_error("GpuState::Initialize: Failed to create "
                                     "and initialize the MPS state.");
        } else
          throw std::runtime_error(
              "GpuState::Initialize: Failed to create the MPS state.");
      } else
        throw std::runtime_error("GpuState::Initialize: Invalid simulation "
                                 "type for initializing the state.");
    }
  }

  void InitializeState(size_t num_qubits,
                       std::vector<std::complex<double>> &amplitudes) override {
    if (num_qubits == 0)
      return;
    Clear();
    nrQubits = num_qubits;
    Initialize();
 
    if (simulationType != SimulationType::kStatevector)
      throw std::runtime_error("GpuState::InitializeState: Invalid simulation "
                               "type for initializing the state.");
 
    if (nrQubits) {
      if (simulationType == SimulationType::kStatevector) {
        state = SimulatorsFactory::CreateGpuLibStateVectorSim();
        if (state)
          state->CreateWithState(
              nrQubits, reinterpret_cast<const double *>(amplitudes.data()));
      }
    }
  }

#ifndef NO_QISKIT_AER
  void InitializeState(size_t num_qubits,
                       AER::Vector<std::complex<double>> &amplitudes) override {
    if (num_qubits == 0)
      return;
    Clear();
    nrQubits = num_qubits;
    Initialize();
 
    if (simulationType != SimulationType::kStatevector)
      throw std::runtime_error("GpuState::InitializeState: Invalid simulation "
                               "type for initializing the state.");
 
    if (nrQubits) {
      if (simulationType == SimulationType::kStatevector) {
        state = SimulatorsFactory::CreateGpuLibStateVectorSim();
        if (state)
          state->CreateWithState(
              nrQubits, reinterpret_cast<const double *>(amplitudes.data()));
      }
    }
  }
#endif

  void InitializeState(size_t num_qubits,
                       Eigen::VectorXcd &amplitudes) override {
    if (num_qubits == 0)
      return;
    Clear();
    nrQubits = num_qubits;
    Initialize();
 
    if (simulationType != SimulationType::kStatevector)
      throw std::runtime_error("GpuState::InitializeState: Invalid simulation "
                               "type for initializing the state.");
 
    if (nrQubits) {
      if (simulationType == SimulationType::kStatevector) {
        state = SimulatorsFactory::CreateGpuLibStateVectorSim();
        if (state)
          state->CreateWithState(
              nrQubits, reinterpret_cast<const double *>(amplitudes.data()));
      }
    }
  }

  void Reset() override {
    if (state)
      state->Reset();
    else if (mps)
      mps->Reset();
  }

  void Configure(const char *key, const char *value) override {
    if (std::string("method") == key) {
      if (std::string("statevector") == value)
        simulationType = SimulationType::kStatevector;
      else if (std::string("matrix_product_state") == value)
        simulationType = SimulationType::kMatrixProductState;
    } else if (std::string("matrix_product_state_truncation_threshold") ==
               key) {
      singularValueThreshold = std::stod(value);
      if (singularValueThreshold > 0.) {
        limitEntanglement = true;
        if (mps)
          mps->SetCutoff(singularValueThreshold);
      } else
        limitEntanglement = false;
    } else if (std::string("matrix_product_state_max_bond_dimension") == key) {
      chi = std::stoi(value);
      if (chi > 0) {
        limitSize = true;
        if (mps)
          mps->SetMaxExtent(chi);
      } else
        limitSize = false;
    }
  }

  std::string GetConfiguration(const char *key) const override {
    if (std::string("method") == key) {
      switch (simulationType) {
      case SimulationType::kStatevector:
        return "statevector";
      case SimulationType::kMatrixProductState:
        return "matrix_product_state";
      default:
        return "other";
      }
    } else if (std::string("matrix_product_state_truncation_threshold") ==
               key) {
      if (limitEntanglement && singularValueThreshold > 0.)
        return std::to_string(singularValueThreshold);
    } else if (std::string("matrix_product_state_max_bond_dimension") == key) {
      if (limitSize && limitSize > 0)
        return std::to_string(chi);
    }
 
    return "";
  }

  size_t AllocateQubits(size_t num_qubits) override {
    if ((simulationType == SimulationType::kStatevector && state) ||
        (simulationType == SimulationType::kMatrixProductState && mps))
      return 0;
 
    const size_t oldNrQubits = nrQubits;
    nrQubits += num_qubits;
    return oldNrQubits;
  }

  size_t GetNumberOfQubits() const override { return nrQubits; }

  void Clear() override {
    state = nullptr;
    mps = nullptr;
    nrQubits = 0;
  }

  size_t Measure(const Types::qubits_vector &qubits) override {
    // TODO: this is inefficient, maybe implement it better in gpu sim
    // for now it has the possibility of measuring a qubits interval, but not a
    // list of qubits
 
    size_t res = 0;
    size_t mask = 1ULL;
 
    DontNotify();
    if (simulationType == SimulationType::kStatevector) {
      // TODO: measure all qubits in one shot?
      for (size_t qubit : qubits) {
        if (state->MeasureQubitCollapse(static_cast<int>(qubit)))
          res |= mask;
        mask <<= 1;
      }
    } else if (simulationType == SimulationType::kMatrixProductState) {
      // TODO: measure all qubits in one shot?
      for (size_t qubit : qubits) {
        if (mps->Measure(static_cast<unsigned int>(qubit)))
          res |= mask;
        mask <<= 1;
      }
    }
 
    Notify();
    NotifyObservers(qubits);
 
    return res;
  }

  void ApplyReset(const Types::qubits_vector &qubits) override {
    DontNotify();
    if (simulationType == SimulationType::kStatevector) {
      for (size_t qubit : qubits)
        if (state->MeasureQubitCollapse(static_cast<int>(qubit)))
          state->ApplyX(static_cast<int>(qubit));
    } else if (simulationType == SimulationType::kMatrixProductState) {
      for (size_t qubit : qubits)
        if (mps->Measure(static_cast<unsigned int>(qubit)))
          mps->ApplyX(static_cast<unsigned int>(qubit));
    }
 
    Notify();
    NotifyObservers(qubits);
  }

  double Probability(Types::qubit_t outcome) override {
    if (simulationType == SimulationType::kStatevector)
      return state->BasisStateProbability(outcome);
    else if (simulationType == SimulationType::kMatrixProductState) {
      const auto ampl = Amplitude(outcome);
      return std::norm(ampl);
    }
 
    return 0.0;
  }

  std::complex<double> Amplitude(Types::qubit_t outcome) override {
    double real = 0.0;
    double imag = 0.0;
 
    if (simulationType == SimulationType::kStatevector)
      state->Amplitude(outcome, &real, &imag);
    else if (simulationType == SimulationType::kMatrixProductState) {
      std::vector<long int> fixedValues(nrQubits);
      for (size_t i = 0; i < nrQubits; ++i)
        fixedValues[i] = (outcome & (1ULL << i)) ? 1 : 0;
      mps->Amplitude(nrQubits, fixedValues.data(), &real, &imag);
    }
 
    return std::complex<double>(real, imag);
  }

  std::vector<double> AllProbabilities() override {
    if (nrQubits == 0)
      return {};
    const size_t numStates = 1ULL << nrQubits;
    std::vector<double> result(numStates);
 
    if (simulationType == SimulationType::kStatevector)
      state->AllProbabilities(result.data());
    else if (simulationType == SimulationType::kMatrixProductState) {
      // this is very slow, it should be used only for tests!
      for (Types::qubit_t i = 0; i < (Types::qubit_t)numStates; ++i) {
        const auto val = Amplitude(i);
        result[i] = std::norm(std::complex<double>(val.real(), val.imag()));
      }
    }
 
    return result;
  }

  std::vector<double>
  Probabilities(const Types::qubits_vector &qubits) override {
    std::vector<double> result(qubits.size());
 
    if (simulationType == SimulationType::kStatevector) {
      for (size_t i = 0; i < qubits.size(); ++i)
        result[i] = state->BasisStateProbability(qubits[i]);
    } else if (simulationType == SimulationType::kMatrixProductState) {
      for (size_t i = 0; i < qubits.size(); ++i) {
        const auto ampl = Amplitude(qubits[i]);
        result[i] = std::norm(ampl);
      }
    }
 
    return result;
  }

  std::unordered_map<Types::qubit_t, Types::qubit_t>
  SampleCounts(const Types::qubits_vector &qubits,
               size_t shots = 1000) override {
    if (qubits.empty() || shots == 0)
      return {};
 
    std::unordered_map<Types::qubit_t, Types::qubit_t> result;
 
    DontNotify();
 
    if (simulationType == SimulationType::kStatevector) {
      std::vector<long int> samples(shots);
      state->SampleAll(shots, samples.data());
 
      for (auto outcome : samples)
        ++result[outcome];
    } else if (simulationType == SimulationType::kMatrixProductState) {
      std::unordered_map<std::vector<bool>, int64_t> *map =
          mps->GetMapForSample();
 
      std::vector<unsigned int> qubitsIndices(qubits.begin(), qubits.end());
 
      mps->Sample(shots, qubitsIndices.size(), qubitsIndices.data(), map);
 
      // put the results in the result map
      for (const auto &[meas, cnt] : *map) {
        Types::qubit_t outcome = 0;
        Types::qubit_t mask = 1ULL;
        for (Types::qubit_t q = 0; q < qubits.size(); ++q) {
          if (meas[q])
            outcome |= mask;
          mask <<= 1;
        }
 
        result[outcome] += cnt;
      }
 
      mps->FreeMapForSample(map);
    }
 
    Notify();
    NotifyObservers(qubits);
 
    return result;
  }

  double ExpectationValue(const std::string &pauliString) override {
    double result = 0.0;
 
    if (simulationType == SimulationType::kStatevector)
      result = state->ExpectationValue(pauliString);
    else if (simulationType == SimulationType::kMatrixProductState)
      result = mps->ExpectationValue(pauliString);
 
    return result;
  }

  SimulatorType GetType() const override { return SimulatorType::kGpuSim; }

  SimulationType GetSimulationType() const override { return simulationType; }

  void Flush() override {}

  void SaveStateToInternalDestructive() override {
    if (simulationType == SimulationType::kStatevector)
      state->SaveStateDestructive();
    else
      throw std::runtime_error(
          "GpuState::SaveStateToInternalDestructive: Invalid simulation type "
          "for saving the state destructively.");
  }

  void RestoreInternalDestructiveSavedState() override {
    if (simulationType == SimulationType::kStatevector)
      state->RestoreStateFreeSaved();
    else
      throw std::runtime_error(
          "GpuState::RestoreInternalDestructiveSavedState: Invalid simulation "
          "type for restoring the state destructively.");
  }

  void SaveState() override {
    if (simulationType == SimulationType::kStatevector)
      state->SaveState();
    else if (simulationType == SimulationType::kMatrixProductState)
      mps->SaveState();
  }

  void RestoreState() override {
    if (simulationType == SimulationType::kStatevector)
      state->RestoreStateNoFreeSaved();
    else if (simulationType == SimulationType::kMatrixProductState)
      mps->RestoreState();
  }

  std::complex<double> AmplitudeRaw(Types::qubit_t outcome) override {
    return Amplitude(outcome);
  }

  void SetMultithreading(bool multithreading = true) override {
    // don't do anything here, the multithreading is always enabled
  }

  bool GetMultithreading() const override { return true; }

  bool IsQcsim() const override { return false; }

  Types::qubit_t MeasureNoCollapse() override {
    if (simulationType == SimulationType::kStatevector)
      return state->MeasureAllQubitsNoCollapse();
    else if (simulationType == SimulationType::kMatrixProductState) {
      Types::qubits_vector fixedValues(nrQubits);
      std::iota(fixedValues.begin(), fixedValues.end(), 0);
      const auto res = SampleCounts(fixedValues, 1);
      if (res.empty())
        return 0;
      return res.begin()
          ->first; // return the first outcome, as it is the only one
    }
 
    throw std::runtime_error(
        "QCSimState::MeasureNoCollapse: Invalid simulation type for measuring "
        "all the qubits without collapsing the state.");
 
    return 0;
  }
 
protected:
  SimulationType simulationType =
      SimulationType::kStatevector; 
 
  std::unique_ptr<GpuLibStateVectorSim>
      state;                         
  std::unique_ptr<GpuLibMPSSim> mps; 
 
  size_t nrQubits = 0; 
  bool limitSize = false;
  bool limitEntanglement = false;
  Eigen::Index chi = 10;              // if limitSize is true
  double singularValueThreshold = 0.; // if limitEntanglement is true
};
 
} // namespace Private
} // namespace Simulators
 
#endif
#endif
#endif