m.compute_from_ll(ll) -- Build motif from an inputed log-likelihood matrix

        (This function reverse-calculates the probability matrix and background frequencies
        that were used to construct the log-likelihood matrix)

def compute_from_ll(self,ll):
        """
        m.compute_from_ll(ll) -- Build motif from an inputed log-likelihood matrix

        (This function reverse-calculates the probability matrix and background frequencies
        that were used to construct the log-likelihood matrix)
        """
        self.ll    = ll
        self.width = len(ll)
        self._compute_bg_from_ll()
        self._compute_logP_from_ll()
        self._compute_ambig_ll()
        self._compute_bits()
        self._compute_oneletter()
        self._maxscore()