Introduction to optimization
and operations research (2019–2020)
Lecturer: Michel Bierlaire, Teaching assistants: Nourelhouda Dougui, Stefano Bortolomiol
Simplex (18 October 2019)
1. What are the basic variables associated with this tableau?
2. What is the vertex xcorresponding to this tableau?
3. What is the value of the objective function at that vertex?
4. What are the reduced costs of the non basic variables?
5. Calculate all basic directions associated with this basic solution, deter-
mine if they are feasible or not, and represent them on a graph. If the
direction is feasible, what is the longest step than can be performed
along the direction?
Question 3:
1. Which of the following statements about a feasible basic solution is true
for a minimization problem?
(a) If ¯c < 0, that is, all reduced costs are negative, the solution is
optimal.
(b) If the values of the basic variables are negative, the solution is
optimal.
(c) If ¯cN>0, that is, the reduced costs of the non basic variables are
positive, the solution is optimal.
2. Consider a linear minimization problem with four variables (x= (x1, x2, x3, x4)T).
In the current iteration of the simplex algorithm, we obtain the reduced
costs vector ¯c= (−1,0,0,0)Tand the upper-right column of the sim-
plex tableau is given by B−1b= (2,4,3)T. Which of the following
propositions is certainly false?
(a) x1enters the basis in the following iteration of the simplex.
(b) x3is a basic variable.
(c) The current solution is not feasible.
3. Which is the feasible basic solution associated with the following sim-
plex tableau?
2