In market making models derived originally from Avellaneda-Stoikov, there is a function lambda that represents the arrival rate of orders. In its prodigy, there are different representations of lambda, some linear, exponential, etc. But, all of these are functions of the difference between the maker's quote and the reference price. How do you calibrate it on initialization?
Also, in a Gueant-Lehalle-Tapia model, how are A and K practically calibrated?