LRP-γ and LRP-Ɛ Rules

Learn about different LRP propagation rules that favor positive contributions and make saliency maps sparser.

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Though the basic propagation rule for LRP works very well in most cases, it can sometimes lead to noisy maps. To remove noise and have sparser saliency maps, we will look into other propagation rules one can use in LRP.

LRP-γ\gamma rule

This LRP rule favors positive contributions rather than negative contributions. The rule can be written as follows:

where wij(l)+=max(0,wij(l))w^{(l)+}_{ij} = \max(0, w^{(l)}_{ij}) ensures that we only give importance to positive contributions, and the parameter γ\gamma controls the amount by which positive contributions are favored. As we increase γ\gamma, the negative contributions start to disappear. This helps us suppress the noise generated by negative contributions and provide stable saliency maps.

LRP-ϵ\epsilon rule

This rule enhances the basic LRP rule by adding a small positive ϵ\epsilon term in the denominator. Mathematically,

The main role of ϵ\epsilon ...