statsmodels.tsa.stattools.acf
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statsmodels.tsa.stattools.acf(x, unbiased=False, nlags=40, qstat=False, fft=False, alpha=None)
[source] -
Autocorrelation function for 1d arrays.
Parameters: x : array
Time series data
unbiased : bool
If True, then denominators for autocovariance are n-k, otherwise n
nlags: int, optional :
Number of lags to return autocorrelation for.
qstat : bool, optional
If True, returns the Ljung-Box q statistic for each autocorrelation coefficient. See q_stat for more information.
fft : bool, optional
If True, computes the ACF via FFT.
alpha : scalar, optional
If a number is given, the confidence intervals for the given level are returned. For instance if alpha=.05, 95 % confidence intervals are returned where the standard deviation is computed according to Bartlett?s formula.
Returns: acf : array
autocorrelation function
confint : array, optional
Confidence intervals for the ACF. Returned if confint is not None.
qstat : array, optional
The Ljung-Box Q-Statistic. Returned if q_stat is True.
pvalues : array, optional
The p-values associated with the Q-statistics. Returned if q_stat is True.
Notes
The acf at lag 0 (ie., 1) is returned.
This is based np.correlate which does full convolution. For very long time series it is recommended to use fft convolution instead.
If unbiased is true, the denominator for the autocovariance is adjusted but the autocorrelation is not an unbiased estimtor.
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