Model compilation internals

Let's look at what happens behind the scenes when model.compile() is called.

Get the optimizer depending on the Backend: 

Here is a list of the optimizers supported:

all_classes = {
'sgd': SGD,
'rmsprop': RMSprop,
'adagrad': Adagrad,
'adadelta': Adadelta,
'adam': Adam,
'adamax': Adamax,
'nadam': Nadam,
'tfoptimizer': TFOptimizer,
}