void vo002_VectorCalculations() { // Operations on RVec instances are made to be *fast* (vectorisation is exploited) // and easy to use. RVecF, RVecD, RVecI, ..., are handy aliases for RVec, RVec, RVec, ... ROOT::RVecF v1{1., 2., 3.}; ROOT::RVecF v2{4., 5., 6.}; // Arithmetic operations are to be intended on pairs of elements with identical index auto v_sum = v1 + v2; auto v_mul = v1 * v2; // Easy to inspect: std::cout << "v1 = " << v1 << "\n" << "v2 = " << v2 << "\n" << "v1 + v2 = " << v_sum << "\n" << "v1 * v2 = " << v_mul << std::endl; // It's also possible to mix scalars and RVecs auto v_diff_s_0 = v1 - 2; auto v_diff_s_1 = 2 - v1; auto v_div_s_0 = v1 / 2.; auto v_div_s_1 = 2. / v1; std::cout << v1 << " - 2 = " << v_diff_s_0 << "\n" << "2 - " << v1 << " = " << v_diff_s_1 << "\n" << v1 << " / 2 = " << v_div_s_0 << "\n" << "2 / " << v1 << " = " << v_div_s_1 << std::endl; // Dot product and the extraction of quantities such as Mean, Min and Max // are also easy to express (see here for the full list: // https://root.cern/doc/master/namespaceROOT_1_1VecOps.html) auto v1_mean = Mean(v1); auto v1_dot_v2 = Dot(v1, v2); std::cout << "Mean of " << v1 << " is " << v1_mean << "\n" << "Dot product of " << v1 << " and " << v2 << " is " << v1_dot_v2 << std::endl; // Most used mathematical functions are supported auto v_exp = exp(v1); auto v_log = log(v1); auto v_sin = sin(v1); std::cout << "exp(" << v1 << ") = " << v_exp << "\n" << "log(" << v1 << ") = " << v_log << "\n" << "sin(" << v1 << ") = " << v_sin << std::endl; // Even an optimised version of the functions is available // provided that VDT is not disabled during the configuration #ifdef R__HAS_VDT auto v_fast_exp = fast_exp(v1); auto v_fast_log = fast_log(v1); auto v_fast_sin = fast_sin(v1); std::cout << "fast_exp(" << v1 << ") = " << v_fast_exp << "\n" << "fast_log(" << v1 << ") = " << v_fast_log << "\n" << "fast_sin(" << v1 << ") = " << v_fast_sin << std::endl; // It may happen that a custom operation needs to be applied to the RVec. // In this case, the Map utility can be used: auto v_transf = Map(v1, [](double x) { return x * 2 / 3; }); std::cout << "Applying [](double x){return x * 2 / 3;} to " << v1 << " leads to " << v_transf << "\n"; #endif }