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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 correlation_matrix(df):
    '''
    Returns a pandas DataFrame with the pair-wise correlations of the columns.

    Args:
        df: pandas DataFrame with columns to run diagnostics on
    '''
    columns = df.columns.tolist()
    corr = pd.DataFrame(
        np.corrcoef(df, rowvar=0), columns=columns, index=columns)
    return corr