Trained models weights, i.e. z and n coefficients
in per-coordinate FTRL-Proximal algorithm.
A frame of shape (nbins, 2 * nlabels), where nlabels is
the total number of labels the model was trained on, and
nbins is the number of bins
used for the hashing trick. Odd and even columns represent
the z and n model coefficients, respectively.
(nbins, 2 * nlabels)