What's the purpose of keras.backend.function()

Question

The Keras manual doesn\'t say too much:

keras.backend.function(inputs, outputs, updates=None)

Instantiates a Keras function.
Arguments
inputs: List of place         


        

Answer 1

I think this function is just used to extract intermediate result. One can refer to the Keras Documentation about "How can I obtain the output of an intermediate layer?"

One simple way is to create a new Model that will ouput the layers that you are interested in:

from keras.models import Model

model = ...  # create the original model

layer_name = 'my_layer'
intermediate_layer_model = Model(inputs=model.input,
                                 outputs=model.get_layer(layer_name).output)
intermediate_output = intermediate_layer_model.predict(data)

Another way is to build a Keras function, which will return the output of a certain layer given input. For example:

from keras import backend as K

# with a Sequential model
get_3rd_layer_output = K.function([model.layers[0].input],
                                  [model.layers[3].output])
layer_output = get_3rd_layer_output([x])[0]

You can used the returned function object get_3rd_layer_output to get the intermediate result of the third layer.