healpy.projaxes.GnomonicAxes.xcorr

GnomonicAxes.xcorr(x, y, normed=True, detrend=<function detrend_none>, usevlines=True, maxlags=10, **kwargs)

Plot the cross correlation between x and y.

Call signature:

xcorr(self, x, y, normed=True, detrend=mlab.detrend_none,
  usevlines=True, maxlags=10, **kwargs)

If normed = True, normalize the data by the cross correlation at 0-th lag. x and y are detrended by the detrend callable (default no normalization). x and y must be equal length.

Data are plotted as plot(lags, c, **kwargs)

Return value is a tuple (lags, c, line) where:

  • lags are a length 2*maxlags+1 lag vector

  • c is the 2*maxlags+1 auto correlation vector

  • line is a Line2D instance

    returned by plot().

The default linestyle is None and the default marker is ‘o’, though these can be overridden with keyword args. The cross correlation is performed with numpy.correlate() with mode = 2.

If usevlines is True:

vlines() rather than plot() is used to draw vertical lines from the origin to the xcorr. Otherwise the plotstyle is determined by the kwargs, which are Line2D properties.

The return value is a tuple (lags, c, linecol, b) where linecol is the matplotlib.collections.LineCollection instance and b is the x-axis.

maxlags is a positive integer detailing the number of lags to show. The default value of None will return all (2*len(x)-1) lags.

Example:

xcorr() is top graph, and acorr() is bottom graph.