siamese_contrastive_loss(ŷ, y; margin = 1, agg = mean)

Return the contrastive loss which can be useful for training Siamese Networks. It is given by

			agg(@. (1 - y) * ŷ^2 + y * max(0, margin - ŷ)^2)                           

Specify margin to set the baseline for distance at which pairs are dissimilar.

Example

			julia> ŷ = [0.5, 1.5, 2.5];

julia> Flux.siamese_contrastive_loss(ŷ, 1:3)
-4.833333333333333

julia> Flux.siamese_contrastive_loss(ŷ, 1:3, margin = 2)
-4.0