LPL - A Mathematical Modeling Language

model cross92 "Hamiltonian Circuit";
  set i,j  "set of vertices of a graph";
  parameter d{i,j} "distance between i and j";
  binary variable x{i,j|i<>j};
  constraint
    A{i}: sum{j} x = 1;
    B{j}: sum{i} x = 1;
    F{i,j|j>i}: x[i,j] + x[j,i] <= 1;
  minimize obj: sum{i,j} d*x;
  Write('minimal tour is: %5.2f\n', obj);
  draw;
  
  model data,D "The star"; 
    i:=1..92;
    set k:=1..#i/4;
    parameter  
      x{k}:=[ 0 -1 -1 -2 -3 -4 -4 -4 -2 -1 -1 -1 -2 -4 -5 -5 -5 -6 -7 -7 -8 -9 -10];
      y{k}:=[10 10  8  7  7  7  6  5  5  4  3  2  1  1  2  3  4  4  4  2  1  1   1];
      X{i}:=(if(i<=23,x[i],  i<=46,-y[i-23],
              i<=69,-x[i-46],  y[i-69])
            +10)/3*2 +.3; 
      Y{i}:=(if(i<=23,y[i],i<=46, x[i-23],
              i<=69,-y[i-46], -x[i-69])
            +10)/3*2 +.3;;
    d{i,j}:= Sqrt((X[j]-X[i])^2+(Y[j]-Y[i])^2);
    d{i,j|d>=3.1}:=99999;
  end

model draw;
    Draw.Scale(40,40);
    Draw.DefFont('Verdana',10);
    {i,j|d<3.1} Draw.Line(D.X[i],D.Y[i],D.X[j],D.Y[j],2);
    {i,j|x}  Draw.Line(D.X[i],D.Y[i],D.X[j],D.Y[j],3,3);
    {i}  Draw.Circle(i&'',D.X,D.Y,.2,1,0);
 end
end

Mathematical Modeling with LPL : Explain and run a Model