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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 plot_correlation(self, freq=None, title=None, figsize=(12, 6), **kwargs):
 """ Utility function to plot correlations. Args: * freq (str):
 Pandas data frequency alias string * title (str):
 Plot title * figsize (tuple (x,y)):
 figure size * kwargs: passed to Pandas' plot_corr_heatmap function """

        if title is None:
            title = self._get_default_plot_title(
                freq, 'Return Correlation Matrix')

        rets = self._get_series(freq).to_returns().dropna()
        return rets.plot_corr_heatmap(title=title, figsize=figsize, **kwargs)