By default, LINGO assumes all variables in a model are continuous. In many applications, fractional values may be undesirable. You won’t be able to hire two-thirds of a person, or sell half an automobile. In these instances, you will want to make use of the general integer variable domain function, @GIN.

The syntax of the @GIN function is:

@GIN( variable_name);

where variable_name is the name of the variable you wish to make general integer. The @GIN function may be used in a model anywhere you would normally enter a constraint. The @GIN function can be embedded in an @FOR statement to allow you to easily set all, or selected, variables of an attribute to be general integers. Some examples of @GIN are:

Example 1:        @GIN( X);

  makes the scalar variable X general integer,

Example 2:        @GIN( PRODUCE( 5));

  makes the variable PRODUCE( 5) general integer,

Example 3:        @FOR( DAYS( I): @GIN( START( I)));

makes all the variables of the START attribute general integer.