docs: public void alias(DMatrixRMaj variable , String name ) {
          if( isReserved(name))
              throw new RuntimeException("Reserved word or contains a reserved character");
          VariableMatrix old = (VariableMatrix)variables.get(name);
          if( old == null ) {
              variables.put(name, new VariableMatrix(variable));
          }else {
              old.matrix = variable;
          }
      }