# scipy.signal.correlation_lags¶

scipy.signal.correlation_lags(in1_len, in2_len, mode='full')[source]

Calculates the lag / displacement indices array for 1D cross-correlation.

Parameters
in1_sizeint

First input size.

in2_sizeint

Second input size.

modestr {‘full’, ‘valid’, ‘same’}, optional

A string indicating the size of the output. See the documentation correlate for more information.

Returns
lagsarray

Returns an array containing cross-correlation lag/displacement indices. Indices can be indexed with the np.argmax of the correlation to return the lag/displacement.

correlate

Compute the N-dimensional cross-correlation.

Notes

Cross-correlation for continuous functions $$f$$ and $$g$$ is defined as:

$\left ( f\star g \right )\left ( \tau \right ) \triangleq \int_{t_0}^{t_0 +T} \overline{f\left ( t \right )}g\left ( t+\tau \right )dt$

Where $$\tau$$ is defined as the displacement, also known as the lag.

Cross correlation for discrete functions $$f$$ and $$g$$ is defined as:

$\left ( f\star g \right )\left [ n \right ] \triangleq \sum_{-\infty}^{\infty} \overline{f\left [ m \right ]}g\left [ m+n \right ]$

Where $$n$$ is the lag.

Examples

Cross-correlation of a signal with its time-delayed self.

>>> from scipy import signal
>>> rng = np.random.RandomState(0)
>>> x = rng.standard_normal(1000)
>>> y = np.concatenate([rng.standard_normal(100), x])
>>> correlation = signal.correlate(x, y, mode="full")
>>> lags = signal.correlation_lags(x.size, y.size, mode="full")
>>> lag = lags[np.argmax(correlation)]


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