MPOValidation.h

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#pragma once
 
#include "../../Types.h"
#include <Eigen/Dense>
#include <algorithm>
#include <limits>
#include <stdexcept>
#include <string>
#include <vector>
 
namespace Simulators::MPOValidation
{
inline void Bits(const std::vector<bool> &bits, size_t width)
{
    if (bits.size() != width)
        throw std::invalid_argument("MPO bit vector must match the register width");
}
 
inline void Pauli(const std::string &pauli, size_t width)
{
    if (pauli.size() != width || pauli.find_first_not_of("IXYZ") != std::string::npos)
        throw std::invalid_argument("Pauli string must have one I/X/Y/Z per qubit");
}
 
inline std::vector<int> Qubits(const Types::qubits_vector &qubits, size_t width)
{
    std::vector<int> result;
    for (auto q : qubits)
    {
        if (q >= width || q > static_cast<size_t>(std::numeric_limits<int>::max()))
            throw std::out_of_range("Target qubit is out of range");
        if (std::find(result.begin(), result.end(), static_cast<int>(q)) != result.end())
            throw std::invalid_argument("Target qubits must be distinct");
        result.push_back(static_cast<int>(q));
    }
    return result;
}
 
inline std::vector<int> Operator(const Types::qubits_vector &qubits, const Eigen::MatrixXcd &matrix, size_t width)
{
    if (qubits.empty() || qubits.size() > 2 || matrix.rows() != (Eigen::Index{1} << qubits.size()) || matrix.cols() != matrix.rows() || !matrix.allFinite())
        throw std::invalid_argument("Operator must be a finite 2x2 or 4x4 matrix matching its targets");
    return Qubits(qubits, width);
}
} // namespace Simulators::MPOValidation