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Klee-Minty Cube


A Klee-Minty cube is a deformed hypercube used to exhibit exponential worst-case behavior of a specified pivot rule for the simplex method in linear programming (Klee and Minty 1972). One standard scaled version maximizes

 sum_(j=1)^n2^(n-j)x_j
(1)

subject to x_j>=0 and

 x_i+sum_(j=1)^(i-1)2^(i-j+1)x_j<=5^i
(2)

for 1<=i<=n. Starting at the origin, the simplex method with Dantzig's largest-positive-reduced-cost rule visits all 2^n vertices, taking 2^n-1 pivots (Vanderbei). This statement concerns that pivot rule and starting point, rather than every algorithm for linear programming.

The table shows the path in two and three dimensions. Labels give the visit order, starting with 0. For display, coordinates are rescaled by u_j=x_j/5^j; the three-dimensional drawing is projected onto a plane. These display transformations do not define a different pivoting problem.

pivot pathdimensionpath length
KleeMintyCubeTable2
n=24 vertices, 3 pivots
KleeMintyCubeTable3
n=38 vertices, 7 pivots

For example, the three-dimensional constraints are

x_1<=5
(3)
4x_1+x_2<=25
(4)
8x_1+4x_2+x_3<=125,
(5)

together with x_1>=0, x_2>=0, and x_3>=0, and the objective is to maximize 4x_1+2x_2+x_3.


See also

Hypercube, Linear Programming, Simplex Method

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References

Klee, V. and Minty, G. J. "How Good Is the Simplex Algorithm?" In Inequalities III. (Ed. O. Shisha). New York: Academic Press, pp. 159-175, 1972.Vanderbei, R. J. "Simplex Challenge-Klee-Minty." https://vanderbei.princeton.edu/JAVA/pivot/kleeminty.html.

Cite this as:

Weisstein, Eric W. "Klee-Minty Cube." From MathWorld--A Wolfram Resource. https://mathworld.wolfram.com/Klee-MintyCube.html

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