code: private void backwardCreateMessage(int edge) {    
          if (!bg.isT1T2(edge) && (bg.t2E(edge) instanceof GlobalFactor)) {
              log.warn("ONLY FOR TESTING: Creating a single message from a global factor: " + edge);
          }
          if (bg.isT1T2(edge)) {
              backwardVarToFactor(edge);
          } else {
              backwardFactorToVar(edge);
          }
          assert !msgsAdj[edge].containsNaN() : "msgsAdj[i] = " + msgsAdj[edge] + "\n" + "edge: " + fg.edgeToString(edge);
      }
docs: Creates the adjoint of the unnormalized message for the edge at time t
  and stores it in msgsAdj[i].