SOS MARKER lines may appear in the COLUMNS section. They contain three fields. The contents of field 1 are ignored. Field 2 must contain the string "'MARKER'" and field 3 contains either the string "'SOSORG'" or the string "'SOSEND'". Note that the single quotes must be part of the fields.

'SOSORG' lines start an SOS section and 'SOSEND' lines terminate an SOS section. SOS sections may not be nested. Each pair of 'SOSORG' and 'SOSEND' lines defines a set of variables; the set contains the variables mentioned in that section. All SOS sets defined in an MPS-format file must be disjoint.

QSopt collects and checks the SOS set information but does not interprete the input otherwise. Thus MPS format files that use this feature can be read and are compatible with QSopt.

See also MPS format COLUMNS section, MPS format MARKER lines, MPS format integer variables, and MPS format definition.