ROOT   6.14/05 Reference Guide
vo002_VectorCalculations.C File Reference

## Detailed Description

In this tutorial we learn how the RVec class can be used to express easily mathematical operations involving arrays and scalars.

using namespace ROOT::VecOps;
void vo002_VectorCalculations()
{
// Operations on RVec instances are made to be *fast* (vectorisation is exploited)
// and easy to use.
RVec<float> v1{1., 2., 3.};
RVec<float> 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.ch/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 utitlity 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
}
Date
May 2018

Definition in file vo002_VectorCalculations.C.