Added Bell state example to examples/exatn-gen.

}

int benchmarkExaTnGen3()

{

 constexpr int NB_QUBITS = 16;

 auto xasmCompiler = xacc::getCompiler("xasm");

 auto ir = xasmCompiler->compile(R"(__qpu__ void bell(qbit q) {

            H(q[0]);

            for (int i = 0; i < 15; i++) {

             CNOT(q[i], q[i + 1]);

            }

           })");

 std::vector<int> bitstring(NB_QUBITS, 0);

 auto program = ir->getComposite("bell");

 auto accelerator =

      xacc::getAccelerator("tnqvm", {{"tnqvm-visitor", "exatn-gen"},

                                     {"exatn-buffer-size-gb", 2},

                                     {"reconstruct-layers", 15},

                                     {"reconstruct-tolerance", 1e-2},

                                     {"max-bond-dim", 1},

                                     {"bitstring", bitstring}});

 auto qreg = xacc::qalloc(NB_QUBITS);

 accelerator->execute(qreg, program);

 qreg->print();

 const auto realAmpl = (*qreg)["amplitude-real"].as<double>();

 const auto imagAmpl = (*qreg)["amplitude-imag"].as<double>();

 std::cout << "Bell state amplitude = {" << realAmpl << "," << imagAmpl << "}\n";

 return 0;

}

int main(int argc, char **argv) {

 xacc::Initialize(argc, argv);

 xacc::set_verbose(true);

 //xacc::setLoggingLevel(2);

 int error_code = 0;

 if(error_code == 0) error_code = benchmarkExaTnGen1();

 if(error_code == 0) error_code = benchmarkExaTnGen2();

 //if(error_code == 0) error_code = benchmarkExaTnGen2();

 if(error_code == 0) error_code = benchmarkExaTnGen3();

 xacc::Finalize();

 return error_code;

}