in the forward pass right and this now gives us a measure of how bad our inverse is right so if G is now an approximate inverse and this now we see here oh okay we we had a ch2 in the forward pass and we basically forward passed and then went through our inverse and we didn't land quite exactly where we started but we know that okay this this is basically the difference between our our inverse our forward inverse H and our true H and then we also back project using G again the desired outcome so we invert the desired outcome