 data with the most recent imputations.

tolerance : float, default=1e-6
    `abs_corr_mat` can have nans, which will be replaced
    with `tolerance`.

Returns
-------
abs_corr_mat : ndarray, shape (n_features, n_features)
    Absolute correlation matrix of `X` at the beginning of the
    current round. The diagonal has been zeroed out and each feature's
    absolute correlations with all others have been normalized to sum
    to 1.
r