Update Trotter example w/ input params to use qcor ArgumentParser

  auto qbits = qalloc(2);

  // Multi-term Hamiltonian

  auto H = X(0) * X(1) + Z(0) + Z(1);

  // Default params:

  double dt = 0.01;

  int nbSteps = 100;

  // Parse user-supplied params (if any)

  std::vector<std::string> arguments(argv + 1, argv + argc);

  for (int i = 0; i < arguments.size(); i++) {

    if (arguments[i] == "-dt") {

      dt = std::stod(arguments[i + 1]);

    }

    if (arguments[i] == "-steps") {

      nbSteps = std::stoi(arguments[i + 1]);

    }

  }

  // dt: Trotter time step size

  // steps: number of steps

  argparse::ArgumentParser program(argv[0]);

  program.add_argument("-dt").default_value(0.01).action(

      [](const std::string &value) { return std::stod(value); });

  program.add_argument("-steps").default_value(100).action(

      [](const std::string &value) { return std::stoi(value); });

  program.parse_args(argc, argv);

  // Get runtime params (if any)

  const double dt = program.get<double>("-dt");

  const int nbSteps = program.get<int>("-steps");

  std::cout << "Trotter for dt = " << dt << "; steps = " << nbSteps << "\n";

  trotter_evolve(qbits, H, dt, nbSteps);

}

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