What is the purpose of bit fail in FANN?

Question

im having a response like below from fann

    Epochs            1. Current error: 0.2500066161. Bit fail 4.
    Epochs           58. Current error: 0.0000930788. Bit fail 0.

what does Bit fail mean here?

Answer 1

The bit fail limit is the maximum difference between the expected and actual output neuron value that is allowed.The default bit fail limit is 0.35. If the difference between the expected and actual output neuron value is more that the bit fail limit, this counts as 1 bit fail. In the sample output you gave, at 58 epochs all the output neurons gave actual outputs close enough to the expected outputs and hence the bit fail was 0 and training stopped. In other words all the training examples gave outputs that were close enough to the expected outputs. During the first epoch, 4 of the training samples gave outputs resulting in bit fails.