so one of the ways to see the intrusion of this model is that we're going to think of the model as one way just informally, not formally, but one way to think about this model is you can think of this factor analysis model as modeling the data from coming from a lower dimensional subspace more or less so the data x here y is approximately on one d line and then plus a little bit of noise - plus a little bit of random noise so the x isn't exactly on this one d line.