Function CopyGradientFromArrays

src/c_api/c_api.cc:1170–1189

Helper function to copy gradient from array interface to linalg::Matrix

// Helper function to copy gradient from array interface to linalg::Matrix
void CopyGradientFromArrays(Context const *ctx, ArrayInterface<2, false> const &i_grad,
                            ArrayInterface<2, false> const &i_hess,
                            linalg::Matrix<GradientPair> *out_gpair) {
  auto grad_is_cuda = ArrayInterfaceHandler::IsCudaPtr(i_grad.data);
  auto hess_is_cuda = ArrayInterfaceHandler::IsCudaPtr(i_hess.data);
  CHECK_EQ(grad_is_cuda, hess_is_cuda) << "gradient and hessian should be on the same device.";

  if (!grad_is_cuda) {
    out_gpair->Reshape(i_grad.Shape<0>(), i_grad.Shape<1>());
    auto h_gpair = out_gpair->HostView();
    DispatchDType(i_grad, DeviceOrd::CPU(), [&](auto &&t_grad) {
      DispatchDType(i_hess, DeviceOrd::CPU(), [&](auto &&t_hess) {
        common::ParallelFor(h_gpair.Size(), ctx->Threads(),
                            detail::CustomGradHessOp{t_grad, t_hess, h_gpair});
      });
    });
  } else {
    CopyGradientFromCudaArrays(ctx, i_grad, i_hess, out_gpair);
  }
}
}  // namespace xgboost

XGB_DLL int XGBoosterTrainOneIter(BoosterHandle handle, DMatrixHandle dtrain, int iter,