Character vector of length one. If "freq" then returns a position frequency matrix (PFM) -
a matrix with occurences of each amino acid in each position.
If "prob" then returns a position probability matrix (PPM) - a matrix with probabilities of occurences of
each amino acid in each position. This is a traditional representation of sequence motifs.
If "wei" then returns a position weight matrix (PWM) - a matrix with log likelihoods of PPM elements.
If "self" then returns a matrix with self-information of elements in PWM.
For more information see https://en.wikipedia.org/wiki/Position_weight_matrix.