Some BOUNDS data lines, aside from changing a variable's bounds, declare the variable to be integral, see MPS format BOUNDS section. Alternatively, a MPS input may contain 'MARKER' lines in the COLUMNS section to declare variables integral.

'MARKER' lines contain three fields. The contents of field 1 are ignored. Field 2 must contain the string ``'MARKER'" and field 3 contains either the string ``'INTORG'" or the string ``'INTEND'". Note that the single quotes must be part of the fields.

A line with ``'INTORG'" starts an integer section and a line with ``'INTEND'" ends an integer section. Integer sections may not be nested. All variables mentioned inside of an integer section are integer (it does not matter whether they are mentioned outside integer sections as well).

The following MPS file excerpt includes line numbers for reference. The COLUMNS section contains two integer sections. The first covers the lines 3-7 and the second covers the lines 11-13. The second MARKER on line 5 is ignored because it tries to start an integer section from within an integer section. The variables x2, x3, and x4 are integer variables since they are mentioned inside an integer section.

 
             1  COLUMNS
             2   x1 obj   1 
             3   mm 'MARKER' 'INTORG' 
             4   x2 obj   1 
             5   mm 'MARKER' 'INTORG' 
             6   x3 obj   1 
             7   mm 'MARKER' 'INTEND' 
             8   x1 row1   3 
             9   x2 row1   5 
            10   x3 row1   5 
            11   mm 'MARKER' 'INTORG' 
            12   x4 obj 1 row1 5 row2 10
            13   mm 'MARKER' 'INTEND'