The simple example of Theano and Lasagne super power

I mentioned in my initial post “Deep Learning Frameworks Overview” that my choice of Deep Learning library is (at least for now)  Theano and Lasagne combination. However, I did not use, in all my post, some most important word: the experiment. So, let’s assume that you have some idea and want to test it quickly. For example, what if we add to a standard CNN (omitted maxpooling for a clarity):


some extra “convolutional branch”, that is concatenated with last but one layer:


This experiment is really easy to do in (based on Theano) Lasagne. I have just added a build_modified_cnn  method to a mnist example (bolded text refers to my “convolutional branch”, rest is the same as a standard build_cnn method):

def build_modified_cnn(input_var=None):
    l_in = lasagne.layers.InputLayer(shape=(None, 1, 28, 28),

    l_conv1 = lasagne.layers.Conv2DLayer(
        l_in, num_filters=32, filter_size=(5, 5),

    l_conv1A = lasagne.layers.Conv2DLayer(
        l_in, num_filters=32, filter_size=(10, 10),

    l_maxpool1A = lasagne.layers.MaxPool2DLayer(l_conv1A, 
        pool_size=(5, 5))

    l_dense1A = lasagne.layers.FlattenLayer(l_maxpool1A)

    l_maxpool1 = lasagne.layers.MaxPool2DLayer(l_conv1, 
        pool_size=(2, 2))

    l_conv2 = lasagne.layers.Conv2DLayer(
        l_maxpool1, num_filters=32, filter_size=(5, 5),
    l_maxpool2 = lasagne.layers.MaxPool2DLayer(l_conv2, 
        pool_size=(2, 2))

    l_dense1 = lasagne.layers.DenseLayer(
        lasagne.layers.dropout(l_maxpool2, p=.5),

    l_concat = lasagne.layers.ConcatLayer([l_dense1, 

    l_dense2 = lasagne.layers.DenseLayer(
        lasagne.layers.dropout(l_concat, p=.5),

    return l_dense2

We see here some standard layers such as Conv2DLayer and MaxPool2DLayer and less standard however self-explanatory ones: FlattenLayer and ConcatLayer. Some results of the test on mnist dataset:

Type Epoch Accuracy Time
Standard CNN 1 56.75 % 6.767s
Standard CNN 30 96.76 % 6.923s
Modified CNN 1 72.51 % 9.552s
Modified CNN 30 96.03 % 9.592s

Not this time. My modification made a significant progress, if we look only at first epoch. However, in general, it learns slower than a standard one. But to see it, I needed only a few minutes of coding – and this is a true power of Theano and Theano-based libs!




4 thoughts on “The simple example of Theano and Lasagne super power

  1. I wonder if the the network *starts* with 2 branches, like this:

    input_A -> [model_path_A] —–
    |—[Linear]–> output_y
    input_B -> [model_path_B] —–

    the input is a tuple (input_A, input_B), how to set the input and train?

    Can you give a new example?



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