When formulating LP's we often found that, strictly, certain variables should have been regarded as taking integer values but, for the sake of convenience, we let them take fractional values reasoning that the variables were likely to be so large that any fractional part could be neglected. Whilst this is acceptable in some situations, in many cases it is not, and in such cases we must find a numeric solution in which the variables take integer values.
Problems in which this is the case are called integer programs (IP's) and the subject of solving such programs is called integer programming (also referred to by the initials IP).
IP's occur frequently because many decisions are essentially discrete (such as yes/no, go/no-go) in that one (or more) options must be chosen from a finite set of alternatives.
Note here that problems in which some variables can take only integer values and some variables can take fractional values are called mixed-integer programs (MIP's).
The LP/IP Solver add-in provides an algorithm that solves Linear and Integer Programming problems. It can be used instead of the Excel solver for the linear models created by the Mathematical Programming add-in. There are no built-in limits for model size. Arrays are dimensioned automatically. For large problems, excessive memory requirements may cause the program to crash or computation time may be large.
When this add-in is installed, a new item appears on the OR_MM menu, LP/IP Solver. This item does not solve models. Rather, models are solved when the user clicks on the Solve button on the linear, integer, or mixed integer model sheets. The LP/IP Solver menu item presents a dialog that sets several parameters related to the solution process and displays. The dialog will appear only when a mathematical programming model constructed with the Math Programming add-in is present on the active worksheet. Otherwise the message below indicates that it is not available.
"This is not a valid worksheet for the LP/IP Solver"
When a valid worksheet is active, choosing the LP/IP Solver menu item presents the dialog below. These options only affect the Jensen LP/IP Solver, and do not affect the Excel Solver.
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