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In GAMS an advanced basis is formed whenever sufficient information is available on the levels and marginals for basis formation. The exact information used are:
| • | Variables with non-zero levels are suggested to be basic unless the levels fall at the upper or lower bounds. |
| • | Variables with non-zero levels equal to their upper or lower bounds – (x.l=x.up or x.l=x.lo) are not suggested to be basic rather being suggested as held at their bound. Variables held at bound should also have non-zero marginals (x.m). |
| • | Variables with zero levels and non-zero marginals are not suggested to be in the basis. |
| • | Constraints with zero marginals have their slacks suggested for inclusion in the basis. |
| • | Constraints with non-zero marginals are treated as binding constraints. |
Such information is typically not available the first time a model is solved unless the user has explicitly provided it.
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