Function VerifySampling

tests/cpp/tree/hist/test_sampler.cc:25–51

namespace xgboost::tree::cpu_impl {
void VerifySampling(float subsample, int sampling_method, bst_target_t n_targets = 1,
                    bool check_sum = true) {
  Context ctx;

  constexpr std::size_t kRows = 4096;
  // Generate random gradients
  auto gpair_container = GenerateRandomGradients(&ctx, kRows, n_targets);
  auto h_gpair = gpair_container.gpair.HostView();

  auto sum_gradients = [&]() {
    auto sum = linalg::Empty<GradientPairPrecise>(&ctx, n_targets);
    cpu_impl::SumGradients(&ctx, h_gpair, sum.HostView());
    return sum.Data()->HostVector();
  };

  auto sum_gpair = sum_gradients();

  TrainParam param;
  param.UpdateAllowUnknown(Args{
      {"subsample", std::to_string(subsample)},
      {"sampling_method", sampling_method == TrainParam::kUniform ? "uniform" : "gradient_based"}});
  Sampler sampler{param};
  sampler.Sample(&ctx, h_gpair);

  auto sum_sampled_gpair = sum_gradients();
  CheckSampling(subsample, n_targets, check_sum, sum_sampled_gpair, sum_gpair, h_gpair);
}

TEST(CpuSampler, NoSampling) {
  constexpr float kSubsample = 1.0f;