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   GGIG project

   GAMS file : EXAMPLES.GMS

   @purpose  : Show some examples how to use globals e.g. found
               in include file generated by GGIG
   @author   : Wolfgang Britz
   @date     : 24.02.16
   @since    :
   @refDoc   :
   @seeAlso  :
   @calledBy :

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*
* ---- these are pseuo-examples of code generated by GGIG
*      They would be found in an included file
*
$setglobal animals on
$setglobal nYears 10

* ----------------------------------------------------------
*
*   Example 1: map a global to a scalar
*
* ----------------------------------------------------------

*
*  --- variant one with acronyms
*
  acronyms on,off;
  scalar p_animals "Flag=on if animals are part of the model" / %animals% /;

  if ( p_animals, display p_animals );

*
*  --- variant two with if statements, no acronym
*
  scalar p_animals2 "Flag=1 if animals are part of the model" / 0 /;
  $$if "%animals%"=="on" p_animals2 = 1;

  if ( p_animals2, display p_animals2 );


* ----------------------------------------------------------
*
*   Example 2: Let a global define which variant of code
*              to use
*
* ----------------------------------------------------------

$iftheni.animals "%animals%" == on
*
*  --- here comes the code with the feed module swtiched on
*
   display "Animals switched on"

$else.animals
*
*  --- here comes the code for the feed module switched off
*
   display "Animals switched off"

$endif.animals

* ----------------------------------------------------------
*
*   Example 3: Let a global define a file to include
*
*               (preferred over 2 especially if several
*                ifthen clauses are nested)
*
*   Note: "typo" "%animals1%" prevents compilation error
*          as "somefile.gms" does not exist
*
* ----------------------------------------------------------

$ifi.animals "%animals1%" == on $include 'someFile.gms'

* ----------------------------------------------------------
*
*   Example 4: Calculate a number from a global
*              and define a set from it
*
* ----------------------------------------------------------

$eval lastYear 1990 + %nYears%

  set years / 1990*%lastYear% /;
  display years;

* ----------------------------------------------------------
*
*   Example 5: Introduce elements into a set
*   depending on a global
*
*   Note: double $$ which allows to move the preprocessor
*         command away from first column available since
*         GAMS 24.0
*
* ----------------------------------------------------------

$onempty

   set acts "Activities" /

      $$if "%animals%"==on pigs,cattle

   /;

$offempty

  display acts;

* ----------------------------------------------------------
*
*   Example 6: Calculate parameters
*              depending on a global,
*              using an acronym
*
* ----------------------------------------------------------

   parameter p_requirements(acts);
*
*  --- code is only an example, calculation does not make sense
*
   p_requirements(acts) $ ( %animals% eq on) = acts.pos;
   display p_requirements;