the method didn't reach this point previously, because it'd throw in line 188. However, now that it does a few lines down the vector will get shuffled to calculate the Pseudo-LH -- but that operation (shuffling the elements of the rows) is not supported by sparse matrices.

I'm not sure if it's worthwhile to change the docstring, since this only materializes `batch_size` rows at a time, which is typically far, far smaller than the whole matrix.