[FIXED] Convert at::Tensor to double in C++ when using LibTorch (PyTorch)

Issue

In the following code, I want to compare the loss (data type at::Tensor) with a lossThreshold (data type double). I want to convert loss to double before making that comparison. How do I do it?

int main() {
    auto const input1(torch::randn({28*28});
    auto const input2(torch::randn({28*28});
    double const lossThreshold{0.05};
    auto const loss{torch::nn::functional::mse_loss(input1, input2)}; // this returns an at::Tensor datatype
    return loss > lossThreshold ? EXIT_FAILURE : EXIT_SUCCESS;
}

Solution

Thanks to GitHub CoPilot which recommended this solution. I guess I should leave my job now. :(

The solution is using the item<T>() template function as follows:

int main() {
    auto const input1(torch::randn({28*28}); // at::Tensor
    auto const input2(torch::randn({28*28}); // at::Tensor
    double const lossThreshold{0.05}; // double
    auto const loss{torch::nn::functional::mse_loss(input1, input2).item<double>()}; // the item<double>() converts at::Tensor to double
    return loss > lossThreshold ? EXIT_FAILURE : EXIT_SUCCESS;
}

Answered By - Raashid