The following model is an example of implementing a binary search in LINGO:

MODEL:

! Illustrates programming looping

 capabilities of LINGO by doing a

 binary search;

SETS:

 S1: X;

ENDSETS

 

DATA:

! The key for which we will search;

 KEY = 16;

! The list (must be in sorted

  increasing order);

 X = 2 7 8 11 16 20 22 32;

ENDDATA

 

! Do a binary search for key;

CALC:

! Set begin and end points of search;

 IB = 1;

 IE = @SIZE( S1);

! Loop to find key;

 @WHILE( IB #LE# IE:

  ! Cut bracket in half;

   LOC = @FLOOR((IB + IE)/2);

   @IFC( KEY #EQ# X(LOC):

     @BREAK; ! Do no more loops;

   @ELSE

     @IFC( KEY #LT# X( LOC):

       IE = LOC-1;

     @ELSE

       IB = LOC+1;

     );

   );

 );

 

 @IFC( IB #LE# IE:

  ! Display key's location;

   @PAUSE( 'Key is at position: ', LOC);

 @ELSE

  ! Key not in list;

   @STOP( ' Key not on list!!!');

 );

ENDCALC

END

Model: LOOPBINS