code: def _compute_logP_from_ll(self):
          
          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
docs: m._compute_logP_from_ll() -- Compute self's logP matrix from the self.ll (log-likelihood)