How can I compare weights of different Keras model

问题:

I've saved numbers of models in .h5 format. I want to compare their characteristics such as weight. I don't have any Idea how I can appropriately compare them specially in the form of tables and figures. Thanks in advance.

回答1:

Weight-introspection is a fairly advanced endeavor, and requires model-specific treatment. Visualizing weights is a largely technical challenge, but what you do with that information's a different matter - I'll address largely the former, but touch upon the latter.

Update: I also recommend See RNN for weights, gradients, and activations visualization.

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Visualizing weights: one approach is as follows:

1. Retrieve weights of layer of interest. Ex: model.layers[1].get_weights()
2. Understand weight roles and dimensionality. Ex: LSTMs have three sets of weights: kernel, recurrent, and bias, each serving a different purpose. Within each weight matrix are gate weights - Input, Cell, Forget, Output. For Conv layers, the distinction's between filters (dim0), kernels, and strides.
3. Organize weight matrices for visualization in a meaningful manner per (2). Ex: for Conv, unlike for LSTM, feature-specific treatment isn't really necessary, and we can simply flatten kernel weights and bias weights and visualize them in a histogram
4. Select visualization method: histogram, heatmap, scatterplot, etc - for flattened data, a histogram is the best bet

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Interpreting weights: a few approaches are:

• Sparsity: if weight norm ("average") is low, the model is sparse. May or may not be beneficial.
• Health: if too many weights are zero or near-zero, it's a sign of too many dead neurons; this can be useful for debugging, as once a layer's in such a state, it usually does not revert - so training should be restarted
• Stability: if weights are changing greatly and quickly, or if there are many high-valued weights, it may indicate impaired gradient performance, remedied by e.g. gradient clipping or weight constraints

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Model comparison: there isn't a way for simply looking at two weights from separate models side-by-side and deciding "this is the better one"; analyze each model separately, for example as above, then decide which one's ups outweigh downs.

The ultimate tiebreaker, however, will be validation performance - and it's also the more practical one. It goes as:

1. Train model for several hyperparameter configurations
2. Select one with best validation performance
3. Fine-tune that model (e.g. via further hyperparameter configs)

Weight visualization should be mainly kept as a debugging or logging tool - as, put simply, even with our best current understanding of neural networks one cannot tell how well the model will generalize just by looking at the weights.

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Suggestion: also visualize layer outputs - see this answer and sample output at bottom.

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Visual example:

from tensorflow.keras.layers import Input, Conv2D, Dense, Flatten
from tensorflow.keras.models import Model

ipt = Input(shape=(16, 16, 16))
x   = Conv2D(12, 8, 1)(ipt)
x   = Flatten()(x)
out = Dense(16)(x)

model = Model(ipt, out)
model.compile('adam', 'mse')

X = np.random.randn(10, 16, 16, 16)  # toy data
Y = np.random.randn(10, 16)  # toy labels
for _ in range(10):
    model.train_on_batch(X, Y)

def get_weights_print_stats(layer):
    W = layer.get_weights()
    print(len(W))
    for w in W:
        print(w.shape)
    return W

def hist_weights(weights, bins=500):
    for weight in weights:
        plt.hist(np.ndarray.flatten(weight), bins=bins)

W = get_weights_print_stats(model.layers[1])
# 2
# (8, 8, 16, 12)
# (12,)

hist_weights(W)

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Conv1D outputs visualization: (source)