Adding slack variables to the output

By default GAMS output contains equation levels.  An equation level is the activity on the left-hand side of an equation.  Most people are not taught such a concept but rather expect to see slack variables.  GAMS will replaces the equation levels with slack variables in the output if one uses the option command:

Option solslack=1

Without this command when solving slack.gms the equation part of the solution is

---- EQU AVAILABLE   RESOURCES AVAILABLE

              LOWER     LEVEL     UPPER    MARGINAL

Land           -INF    800.000   800.000   118.700

Spring Labor   -INF   3114.000  4800.000      .

Fall Labor     -INF   3300.000  3300.000     4.600

but with it

              LOWER     SLACK     UPPER    MARGINAL

Land           -INF       .      800.000   118.700

Spring Labor   -INF   1686.000  4800.000      .

Fall Labor     -INF       .     3300.000     4.600