def _compute_logP_from_ll(self):
        """
        m._compute_logP_from_ll() -- Compute self's logP matrix from the self.ll (log-likelihood)
        """
        log = math.log
        logP = []
        for i in range(self.width):
            D = {}
            for L in ACGT:
                ''' if   ll = log(p/b) then
                       2^ll = p/b
                  and    ll = log(p) - log(b)
                  so log(p) = ll + log(b)'''
                #Pij = pow(2.0, self.ll[i][letter]) * self.background[letter]
                D[L] = self.ll[i][L] + log(self.background[L])/log(2.)
            logP.append(D)
        self.logP = logP