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I am building a neural network (using tensorflow/keras) that attempts to classify into one of 5 categories (0, 1, 2, 3, 4). I have been using sparse categorical cross-entropy as my loss function. This works as is expected, but my data is "somewhat" ordinal. When a label is 3 a prediction of 2 is much better than a prediction of 1 (which is better than 0, etc.). Basically, the loss function would use the predicted probabilities of the tensorflow model rather than the predicted classification ([.1, .2, .2, .4, .1] rather than 3).

Is there any loss function that takes advantage of this?

I could imagine something like:

enter image description here

where 𝑁 is the number of samples, 𝑦𝑖,𝑗=𝑖 is the probability of predicting the correct class, 𝑦𝑖,|π‘–βˆ’π‘—|=1 is the probability of predicting one class off, etc.

In short, there is a penalty for the probability of prediction one unit away, a larger penalty for two units away, and so on. However, I am unsure of how to implement this myself in tensorflow as a custom loss function because most loss functions I have seen do not utilize the predicted probabilities. Any help pointing me to a loss function that accomplishes this or help on a way to implement something like the above would be appreciated. As well as any dialogue on alternatives.

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Traditional neural networks do not approximate a probability distribution. While some outputs (softmax) or loss functions can look like probabilities or using techniques from statistics the model remains a point approximation with fixed weight values. This means you cannot use the model to approximate the uncertainty in a Bayesian way. To introduce uncertainty into the model, I recommend Bayesian Neural Networks and/or Bayesian Dropout.

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  • $\begingroup$ Logistic regression estimates a probability. Why do you say that more complicated neural networks do not? $\endgroup$
    – Dave
    Jul 15, 2021 at 20:30

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