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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def profile(self):
 """Measure of bandedness, also known as 'envelope size'."""

    leftmost_idx = np.argmax(self.matrix('dense').astype(bool), axis=0)
    return (np.arange(self.num_vertices()) - leftmost_idx).sum()