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import numpy as np
def delta(feat, window):
assert window > 0
delta_feat = np.zeros_like(feat)
for i in range(1, window + 1):
delta_feat[:-i] += i * feat[i:]
delta_feat[i:] += -i * feat[:-i]
delta_feat[-i:] += i * feat[-1]
delta_feat[:i] += -i * feat[0]
delta_feat /= 2 * sum(i ** 2 for i in range(1, window + 1))
return delta_feat
def add_deltas(x, window=2, order=2):
feats = [x]
for _ in range(order):
feats.append(delta(feats[-1], window))
return np.concatenate(feats, axis=1)
class AddDeltas(object):
def __init__(self, window=2, order=2):
self.window = window
self.order = order
def __repr__(self):
return "{name}(window={window}, order={order}".format(
name=self.__class__.__name__, window=self.window, order=self.order
)
def __call__(self, x):
return add_deltas(x, window=self.window, order=self.order)
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