To begin, click on the
link at left. This will pop up a
new tab with a simple form, prompting you to choose whether the problem
consists of inequalities or equalities. A third option, Empty,
allows you to simply paste an existing tableau that you might have
copied from Maple or a word processing program.
In this case you should enter the value of the basic coefficient,
which is set to 1 as the default otherwise.
After you have selected the type of constraints in your problem, a
few more prompts show up. One of these allows you to choose whether
the problem is a linear optimization problem (LOP) or a system of
constraints. The only difference between the two types of problems is
that a LOP will contain a z-column and an objective row,
whereas a system will not. You are also prompted to enter the number
of variables and constraints in the problem, after which you should
click Done.
At this point a table appears with the slack variable coefficients
filled in (and the z-column as well if the problem is a LOP).
The table of numbers in the middle represents a tableau which can be
edited or pivoted on at any time. The tab and arrows keys move from
one cell to another to allow data entry and editing --- experiment
with them to see how they wrap around horizontally and vertically.
The
to the left and above the tableau are used for popping up menus.
In order to pop-up a menu, simply right-click any button or entry.
The button above and to the left is called the tableau button,
the buttons directly above the tableau are called column buttons,
and the buttons directly to the left of the tableau are called row
buttons.
Pivoting can be accomplished simply by double-clicking on the entry
on which you wish to pivot. The resulting tableau will appear beneath
the current tableau, and the page will automatically scroll to show only
the resulting tableau. (Scrolling between tableau can be useful for
class discussions when discovering or witnessing patterns. Also, one can
scroll up to a prior tableau and pivot on it successfully.) Note that
integer arithmetic is used, so that one needs to divide by the basic
coefficient in order to calculate curent basic and objective values.
It is also visually useful to draw lines between various rows, to separate
constraints from the objective row, for example (and also original
constraints from new valid inequalities from cutting planes), and between
various columns, to separate problem variables, slack variables, and the
b-column. This can be accomplished by clicking on the black
lines between the buttons.
Saving a sequence of tableaux is accomplished by saving the page
in your browser. Later, when you open that page in your browser you
will see the sequence but it is not an active page (you will not be
able to pivot or use any buttons).
|