[duvenaud]

This is simply wrong. Backprop has the same asymptotic time complexity as forward.

[bobmarleybiceps]

I think they're misusing "forward propagation" and "backward propagation" to be basically mean "post training inference" and "training". they seem to be assuming n iterations of the backward pass, which is why it's larger...

[vrighter]

n iterations would be a constant factor, which is omitted from asymptotic complexity