//######################################################################
//#  generate trellis representation of FSM as an SVG file
//######################################################################
void fsm::print_trellis( std::string filename ,int number_stages)
{
   std::ofstream trellis_fname (filename.c_str());
   if (!trellis_fname) {std::cout << "file not found " << std::endl ; exit(-1);}
   const int TRELLIS_Y_OFFSET = 30;
   const int TRELLIS_X_OFFSET = 20;
   const int STAGE_LABEL_Y_OFFSET = 25;
   const int STAGE_LABEL_X_OFFSET = 20;
   const int STATE_LABEL_Y_OFFSET = 30;
   const int STATE_LABEL_X_OFFSET = 5;
   const int STAGE_STATE_OFFSETS = 10;
//   std::cout << "################## BEGIN SVG TRELLIS PIC #####################" << std::endl;
   trellis_fname << "<svg viewBox = \"0 0 200 200\" version = \"1.1\">" << std::endl;

    for(unsigned int stage_num = 0;stage_num < number_stages;stage_num ++){
    // draw states
      for (unsigned int state_num = 0;state_num < d_S ; state_num ++ ) {
        trellis_fname << "<circle cx = \"" << stage_num * STAGE_STATE_OFFSETS + TRELLIS_X_OFFSET << 
        "\" cy = \"" << state_num * STAGE_STATE_OFFSETS + TRELLIS_Y_OFFSET << "\" r = \"1\"/>" << std::endl;
      //draw branches
        if(stage_num != number_stages-1){
          for(unsigned int branch_num = 0;branch_num < d_I; branch_num++){
            trellis_fname << "<line x1 =\"" << STAGE_STATE_OFFSETS * stage_num+ TRELLIS_X_OFFSET  << "\" ";
            trellis_fname << "y1 =\"" << state_num * STAGE_STATE_OFFSETS + TRELLIS_Y_OFFSET<< "\" ";
            trellis_fname << "x2 =\"" <<  STAGE_STATE_OFFSETS *stage_num + STAGE_STATE_OFFSETS+ TRELLIS_X_OFFSET << "\" ";
            trellis_fname << "y2 =\"" << d_NS[d_I * state_num + branch_num] * STAGE_STATE_OFFSETS + TRELLIS_Y_OFFSET << "\" ";
            trellis_fname << " stroke-dasharray = \"3," <<  branch_num << "\" ";
            trellis_fname << " stroke = \"black\" stroke-width = \"0.3\"/>" << std::endl;
          }
        }
      }
    }
  // label the stages
  trellis_fname << "<g font-size = \"4\" font= \"times\" fill = \"black\">" << std::endl;
  for(unsigned int stage_num = 0;stage_num < number_stages ;stage_num ++){
    trellis_fname << "<text x = \"" << stage_num * STAGE_STATE_OFFSETS + STAGE_LABEL_X_OFFSET << 
      "\" y = \""  << STAGE_LABEL_Y_OFFSET  << "\" >" << std::endl;
    trellis_fname << stage_num <<  std::endl;
    trellis_fname << "</text>" << std::endl;
  }
  trellis_fname << "</g>" << std::endl;

  // label the states
  trellis_fname << "<g font-size = \"4\" font= \"times\" fill = \"black\">" << std::endl;
  for(unsigned int state_num = 0;state_num < d_S ; state_num ++){
    trellis_fname << "<text y = \"" << state_num * STAGE_STATE_OFFSETS + STATE_LABEL_Y_OFFSET << 
      "\" x = \""  << STATE_LABEL_X_OFFSET  << "\" >" << std::endl;
    trellis_fname << state_num <<  std::endl;
    trellis_fname << "</text>" << std::endl;
  }
  trellis_fname << "</g>" << std::endl;


  trellis_fname << "</svg>" << std::endl;
//  std::cout << "################## END SVG TRELLIS PIC ##################### " << std::endl;
  trellis_fname.close();
}