This is the Simplex Java Applet!
You are person number
to access this page since September 26, 1996.
Applet Controls
What's New?
This version of the Simplex tool was installed on January 28, 1997.
Please contact us if you encounter any problems with the new version.
The
old version is still available.
- Improved handling of artificial variables
- New version of matrix factorization
How the applet works
There are a series of windows that take you through the
simplex method.
- New Problem - This button opens up the window that gets
everything started.
- Quit - This button closes all windows that are currently on
the screen.
- About- This button brings up an about window for this applet.
After you click the New Problem button, a window pops up
asking you to enter the number of constraints and number of variables
for your linear program. You can enter values between 2 and 7 for
both.
Next a window will pop up that allows you to enter the
objective function and constraints. You only have to enter
nonzero entries! On this window you have three buttons.
- Preprocess - Press this button to start solving your linear
program.
- Reset - This button allows you to start over with a problem
of the same dimensions. The old values are not wiped out. This
button is good if you make a slight mistake entering your linear
program.
- Clear - This button clears all the numbers. The Clear
button is only enabled when it is possible to enter the numbers of the
linear program.
Once Preprocess is pressed another window comes up with your
preprocessed linear program. There are two buttons on this window.
- Step - This button takes you step-by-step through the
two-phase revised simplex method.
- Iterate - This button takes you through a whole iteration
of the two-phase revised simplex method. This button is disabled if
you are in the middle of the process of stepping through the simplex
method.
At one point in the stepping process, you will have the
opportunity to choose the incoming variable. If the problem has not
yet been solved, you will get the message "Test for Optimality: Not
Optimal! Pick entering Variable." At this point, radio checkboxes
located beneath the variables will become enabled if that variable is
eligible to enter the basis. The variable with the most negative
reduced cost is choosen by default.
A Small Example Problem
Here is a small problem which demonstrates the applet. This problem
requires both phases of the simplex method (the feasibility phase and
the optimality phase).
2 constraints and 2 variables
Minimize 1 x1 + 3 x2
Subject to:
2 x1 + 4 x2 >= 8
-1 x1 + 3 x2 <= 2
x>= 0
Note: During the first iteration, you have the choice of x1
(with reduced cost = -2) or x2 (with reduced cost = -4) to
enter the basis.
Potentially Confusing Points
When the iterate button is pressed, the information you see is what
was used in the previous iteration. The reduced costs correspond to
the last iteration. This is why one of the basic variables has a
reduced cost associated with it. The number you see is the old
reduced cost.
See the source code for the applet.
Comments and Suggestions
This tool is new, and we need your feedback to know how to make it
more useful.
Give us your comments.
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