Description

This test is for a problem we encountered with 21.0.
if(...,
  loop(...,
  solve ..
x(...  );

on the second round we got the wrong data because the
driving loop index got messed up.

Small Model of Type : GAMS

Category : GAMS Test library

Main file : nest1.gms

$Title nested If - loop - solve test with alias (NEST1,SEQ=62)
$Ontext
This test is for a problem we encountered with 21.0.
if(...,
  loop(...,
  solve ..
x(...  );

on the second round we got the wrong data because the
driving loop index got messed up.

$offtext

  Sets
       i   canning plants   / seattle, san-diego /
       j   markets          / new-york, chicago, topeka / ;

  Parameters

       a(i)  capacity of plant i in cases
         /    seattle     350
              san-diego   600  /

       b(j)  demand at market j in cases
         /    new-york    325
              chicago     300
              topeka      275  / ;

  Table d(i,j)  distance in thousands of miles
                    new-york       chicago      topeka
      seattle          2.5           1.7          1.8
      san-diego        2.5           1.8          1.4  ;

  Scalar f  freight in dollars per case per thousand miles  /90/ ;

  Parameter c(i,j)  transport cost in thousands of dollars per case ;

            c(i,j) = f * d(i,j) / 1000 ;

  Variables
       x(i,j)  shipment quantities in cases
       z       total transportation costs in thousands of dollars ;

  Positive Variable x ;

  Equations
       cost        define objective function
       supply(i)   observe supply limit at plant i
       demand(j)   satisfy demand at market j ;

  cost ..        z  =e=  sum((i,j), c(i,j)*x(i,j)) ;

  supply(i) ..   sum(j, x(i,j))  =l=  a(i) ;

  demand(j) ..   sum(i, x(i,j))  =g=  b(j) ;

  Model transport /all/ ;

option limcol=0,limrow=0,solprint=off;

parameter dd;

scalar mode / 1/, cnt / 0 /;

set k / 1*4 /, kval(k) ;  alias(k,kk);

if(mode=1,
   loop(kk ,
   kval(kk) = yes;
   display kval;
   Solve transport using lp maximizing z ;
   cnt := cnt + 1;
   c(i,j) = c(i,j)*1.1; );
   dd(i) = 10 );

set diff; diff(k) = yes - kval(k);

abort$((cnt <> card(k)) or card(diff)) 'the loop did not run correctly',kval,diff;