ROOT::RVecF phis = {0.0, 1.0, -0.5, M_PI + 1.0};
auto idx = Combinations(phis, 2);

auto phi1 = Take(phis, idx[0]);
auto phi2 = Take(phis, idx[1]);
auto dphi = DeltaPhi(phi1, phi2);

std::cout << "DeltaPhi(phi1 = " << phi1 << ",\n"
          << "         phi2 = " << phi2 << ")\n"
          << " = " << dphi << "\n";

ROOT::RVecF etas = {2.4, -1.5, 1.0, 0.0};

auto eta1 = Take(etas, idx[0]);
auto eta2 = Take(etas, idx[1]);
auto dr = DeltaR(eta1, eta2, phi1, phi2);

std::cout << "\nDeltaR(eta1 = " << eta1 << ",\n"
          << "       eta2 = " << eta2 << ",\n"
          << "       phi1 = " << phi1 << ",\n"
          << "       phi2 = " << phi2 << ")\n"
          << " = " << dr << "\n";

ROOT::RVecF pt3 = {40, 20, 30};
ROOT::RVecF eta3 = {2.5, 0.5, -1.0};
ROOT::RVecF phi3 = {-0.5, 0.0, 1.0};
ROOT::RVecF mass3 = {10, 10, 10};

ROOT::RVecF pt4 = {20, 10, 40};
ROOT::RVecF eta4 = {0.5, -0.5, 1.0};
ROOT::RVecF phi4 = {0.0, 1.0, -1.0};
ROOT::RVecF mass4 = {2, 2, 2};

auto invMass = InvariantMasses(pt3, eta3, phi3, mass3, pt4, eta4, phi4, mass4);

std::cout << "\nInvariantMass(pt1 = " << pt3 << ",\n"
          << "              eta1 = " << eta3 << ",\n"
          << "              phi1 = " << phi3 << ",\n"
          << "              mass1 = " << mass3 << ",\n"
          << "              pt2 = " << pt4 << ",\n"
          << "              eta2 = " << eta4 << ",\n"
          << "              phi2 = " << phi4 << ",\n"
          << "              mass2 = " << mass4 << ")\n"
          << " = " << invMass << "\n";

auto invMass2 = InvariantMass(pt3, eta3, phi3, mass3);

std::cout << "\nInvariantMass(pt = " << pt3 << ",\n"
          << "              eta = " << eta3 << ",\n"
          << "              phi = " << phi3 << ",\n"
          << "              mass = " << mass3 << ")\n"
          << " = " << invMass2 << "\n";