Common Causes of Confusion
It should be noted that most of the library routines described above and in chapter Console and Library Functions, which modify the matrix will not work on a presolved matrix. The only exception is inside a callback for a MIP solve, where cuts may be added or variable bounds tightened (using XPRSchgbounds). Any of these functions expect references to the presolved problem. If one tries to retrieve rows, columns, bounds or the number of these, such information will come from the presolved matrix and not the original. A few functions exist which are specifically designed to work with presolved and scaled matrices, although care should be exercised in using them. Examples of these include the commands XPRSgetpresolvesol, XPRSgetpresolvebasis, XPRSgetscaledinfeas, XPRSloadpresolvebasis and XPRSloadpresolvedirs.
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