Larger Image    When the QSopt interface starts it displays empty input, status, and solution panes. The input pane's title LP input indicates that the interface expects that a linear programming problem will be defined in LP format. At this point a problem can be edited from scratch or a predefined problem can be loaded from a file by using the Open option from the File Menu.
 
Larger Image    To define a simple problem let us assume the user types the following lines into the input pane:
   MIN
       x + 2y
   Subject To
       x <=10
       2x - 3y = 30
and choses Check Format from the Edit menu. The QSopt gui reports a warning and an error:
   \\\ LP Warning: Empty obj name; using "obj".
   \\\ LP Error: Missing "End" at end of file.
in the input pane and writes messages to the status pane indicating that the input did not correctly define a linear programming problem.
 
Larger Image   The warning can safely be ignored, the error is easily corrected by added End at the end of the input. The problem can now be solved by using the Solve option from the Solver menu, by typing Ctrl-R, which is the solve commands shortcut, or by clicking the go button on the toolbar. QSopt's solver reports its progress while executing by printing messages to the status pane. In this case the problem is quickly determined to be infeasible.
 
Larger Image   The problem can be 'fixed' to be feasible by changing the second constraint to read 2.0 x + 3.0 y = 30.0. To get rid of the warnings we reformat the input by using the Reformat as LP option on the Edit menu. QSopt fills in all default names such as obj for the objective function and c1, c2 for the constraint names. Finally rerunning the solver produces a solution. The ojective value and the non-zero primal solution values are displayed in the solution pane to the right of QSopt's window.
 
Larger Image   Of course QSopt can also solve larger instances of linear problems as well. If a complex problem is given, QSopt's solver may take a noticable amount of time to come to a solution. QSopt blocks most inputs while the solver executes. It is for example not possible to edit a linear problem while the solver is running. Note that the input pane and most toolbar buttons are greyed during solver execution. The only active button aside from the help button is the red cross, which when clicked executes the Stop Solver command. As the name suggests, it is used to abort an executing solver.
 
Larger Image   Eventually this large problem is solved. To see the dual solution values the user can choose Show Dual Solution from the Solver menu. Note that QSopt still prohibits the user from editing the input. It does so for all inputs that exceed 20000 lines. Thus very large files may be read and the problems they define may be solved but they can not be edited.
 
To browse the Windows interface help files click on QSopt Main Help Index.