1

I am trying to define some sets dynamically with set operations (in my case the "-" operation). However, the "-" operation seems to apply only during the execution phase, and when using this set when defining other sets, gams fails with the following error: 644 set.ident or #.ident has undefined data. I believe the issue is that the set defined with the minus operation does not get created until the execution phase.

I could not find a solution to create the set during the compilation phase. Any help appreciated, with a minimal reproducible example below.

set alphabet /
"a"
"b"
"c"
/;

set a(alphabet) /
"a"
/;

sets bc(alphabet);
bc(alphabet) = alphabet(alphabet) - a(alphabet);

set test1(alphabet)
/
#a
/;

set test2(alphabet)
/
#a
#bc
/;

set test3(alphabet)
/
set.a
/;

set test4(alphabet)
/
set.a
set.bc
/;
Jon
  • 351
  • 2
  • 10

1 Answers1

1

You are right, "bc(alphabet) = alphabet(alphabet) - a(alphabet);" is an execution time statement. Doing a set subtraction at compile time in GAMS directly, is not so easy (in contrast to a set addition, which works). But if you use a recent GAMS system (24.9), you could use the new embedded code facility to do this:

set alphabet /
"a"
"b"
"c"
/;

set a(alphabet) /
"a"
/;

sets bc(alphabet);

$onEmbeddedCode Python:
  gams.set("bc", list(set(gams.get("alphabet")) - set(gams.get("a"))))
$offEmbeddedCode bc

I hope that helps! Lutz

Lutz
  • 2,197
  • 1
  • 10
  • 12
  • thanks for the tip, although seems a bit overkill to use python just to do this... should be a feature in gams – Jon Oct 19 '17 at 07:03