to encode our data notice two ways you can prove Cal is positive we can prove it because we know every encoding has to be hired Andrew could call it done this means that this thing is positive because we know that already or you could prove me from first principles using Jensen's inequality which is shown at the bottom here but so we also will pay a price corresponding to the KL divergence so the better our generic model is the better our encoding scheme can be and so when we think about including with generative models there's