reconstruct its own input right so you feed a data in here you get data out here and then your error the error signal it will be your difference to your original input now the usually when we train autoencoders in deep learning we also train this by back prop right we see then this error here and this goes back but if you just think of single layer autoencoders so um let's let's go over here single layer auto-encoder with let's say the the same number of the same number of units in this in this layer what you'll have is so this this