solver:here

# Modified version of model library example DICE

```\$title Modified version of model library example DICE
\$Ontext

Modified version of model library example
"Non-transitive Dice Design (DICE,SEQ=176)".
This model uses the GAMS BCH facility with GAMS/CPLEX in order to
save incumbent solutions in GDX files during the solution process.

Probabilistic dice - an example of a non-transitive relation.
We want to design a set of dice with an integer number on each face
such that on average dice1 beats dice2, and dice2 on average beats
dice3 etc, but diceN has to beat dice1.

MIP codes behave very erratic on such a problem and slight
reformulations can result in dramatic changes in performance. Also
note the face value will be integers automatically.

Gardner, M, Scientific American.

Robert A Bosh, Mindsharpener, Optima, MP Society Newsletter, Vol 70,
June 2003, page 8-9

Robert A Bosh, Monochromatic Squares, Optima, MP Society Newsletter,
Vol 71, March 2004, page 6-7

\$Offtext

sets    f    faces on a dice  / face1*face6 /
dice number of dice   / dice1*dice3 / ;

scalars flo  lowest face value  / 1 /
fup  highest face value
wn   wins needed - possible bound ;

fup = card(dice) * card(f);

wn = floor(0.5 * sqr(card(f))) + 1;

alias(f,fp);
alias(dice,dicep);

variables  wnx               number of wins
fval(dice,f)      value of dice - will be integer
comp(dice,f,fp)   one if f beats fp ;
binary variable comp;

fval.lo(dice,f) = flo;
fval.up(dice,f) = fup;

fval.fx("dice1","face1") = flo;

equation eq1(dice)       count the wins
eq3(dice,f,fp)  definition of non-transitive relation
eq4(dice,f)     different face values for a single dice;

eq1(dice).. sum((f,fp), comp(dice,f,fp)) =e= wnx;

eq3(dice,f,fp) .. fval(dice,f) + (fup-flo)*(1-comp(dice,f,fp)) =g= fval(dice++1,fp) + 1;

eq4(dice,f-1) .. fval(dice,f-1) + 1 =l= fval(dice,f);

model xdice /all /;

\$if set nosolve \$exit

xdice.reslim = 20;
xdice.optfile=1;
option mip=cplex;
solve xdice using mip max wnx;

option fval:0; display wn,fval.l;

parameter rep1 Chance of winning against next;
rep1(dice,f) = 100*sum(fp, comp.l(dice,f,fp)) / card(f);
rep1(dice,'chance') = sum(f, rep1(dice,f))/card(f);
option rep1:0; display rep1;

* Write incumbent solutions with objective value>15 to a GDX file during the
* solution process by utilizing GAMS BCH facility (www.gams.com/docs/bch.htm).
\$onecho > cplex.opt
userincbicall reportsol.gms lo=2
\$offecho
\$onecho >reportsol.gms
variable wnx;
\$gdxin bchout_i.gdx 