How to Edit and Solve a linear problem

The QSopt interface starts out with an empty document, which is displayed in its Input pane. This document describes a linear problem in LP Format or MPS Format. Which of these two formats is currently 'active' is noted in the Input pane's title bar.

By default QSopt expects its document to be defined in LP format. So to try a simple problem, enter the following text into the Input pane:

        MIN 
                x + 2y
        Subject To 
                x <= 10 
                2x - 3y = 30
        End

You can solve the problem by choosing the Solve command from the the Solver menu or toolbar. QSopt parses the active document and prints the following warnings lines to the Status pane:

 
        Parsing Problem.
        Data Warning: Setting problem name to "unnamed".
        Data Warning: Generating names for unnamed rows.
        The problem unnamed contains 2 rows and 2 variables.

QSopt does not find any errors in the above document and proceeds to solve the problem. It uses the current solver parameters to decide which simplex method and which pricing strategy to use. The default settings are to use the primal simplex with Steep pricing. To change the solver paremeters use the Set Parameters command from the Solver menu.

QSopt blocks most input from the user while the solver executes. For example, the user may not edit the current document in any way. QSopt prints the solution values to the solution pane and the document becomes editable again once the solver finishes, that is as soon as it finds an optimal solution or establishes that the problem is infeasible or unbounded.

QSopt can abort the solver in the middle of its execution by the Stop command from the Solver menu or toolbar.

If you are curious what row names QSopt generated for your problem simply reformat the document. Try the Reformat as LP command from the Edit menu. This command generates and displays a pretty printed version of your problem and includes all optional information such as row and problem names. The reformat commands are also a convenient method of switching between LP and MPS format.

QSopt can not solve the problem when you enter an incorrect problem that is in cases where your document violates the currently active format. QSopt inserts error messages and warnings in the input pane as red comment lines. Some errors and warnings are not tied to a particular input location; these are printed to the Status pane. When QSopt parses the document again it simultaneously removes the 'old' error messages while inserting the 'new' messages. Reparsing the document is automaticallt triggered when running the Solve command. If you want to check the correctness of your document without running the solver you may run the Check Format command from the Edit menu.