Quick start - Gams

The columns associated with each entry have the following meaning,
Notes
Variable marker ----
VAR - Variable identifier
Lower bound (.lo) – often zero or minus infinity
Level value (.l) – solution value.
Upper bound (.up) – often plus infinity
Marginal (.m) – reduced cost which does not convey much information in the non
optimization cases,
The numbers are printed with fixed precision, but the values are returned within GAMS
have full machine accuracy.
The single dots '.' represent zeros.
If present EPS is the GAMS extended value that means very close to but different from
zero.
It is common to see a marginal value given as EPS, since GAMS uses the convention that
marginals are zero for basic variables, and nonzero for others.
EPS is used with non-basic variables whose marginal values are very close to, or actually,
zero, or in nonlinear problems with superbasic variables whose marginals are zero or very
close to it.
For models that are not solved to optimality, some items may additionally be marked
with the following flags.
Flag Description
Infes The item is infeasible. This mark is made for any entry whose level
value is not between the upper and lower bounds.
Nopt The item is non-optimal. This mark is made for any non-basic
entries for which the marginal sign is incorrect, or superbasic ones
for which the marginal value is too large.
Unbnd The row or column that appears to cause the problem to be
unbounded.
Exploiting algebra
By its very nature GAMS is an algebraic language. The above examples and discussion are not
totally exploitive of the algebraic capabilities of GAMS. Now let me introduce more of the
GAMS algebraic features.
Equation writing – sums
Courtesy of B.A. McCarl, October 2002 23