Determining rows and determining columns
Normally, Xpress-SLP automatically identifies if the constraint selected as determining row for a variable defines the value of the SLP variable which it determines or not. However, in certain situations, the value of a single another column determines if the determing row defines the variable or not; such a column is called the determining column for the variable.
This situation is typical when the determined and determining column form a bilinear term: x * y + F( Z ) = 0 where y is the determined variable, Z is a set of other variables not including x or y, and F is an arbitrary function; in this case x is the determining column. These variable pairs are detected automatically. In case the absolute value of x is smaller than XSLP_DRCOLTOL, then variable y will not be cascaded, instead its value will be fixed and kept at its current value until the value of x becomes larger than the threshold.
Alternatively, the handling of variables for which a determining column has been identified can be customized by using a callback, see XSLPsetcbdrcol.
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