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Lecture 6 Simplex Method: Artifical Starting Solution and ...

Lecture 6 Simplex Method: Artifical Starting Solutionand Some Special CasesSeptember 4, 2009 Lecture 6 Outline: Initial table vs initial Simplex table Artificial start: Two-phase method Special cases: Degeneracy Multiple optimal solutions Infinite optimal value Infeasibility of the problemOperations Research Methods1 Lecture 6 Simplex method: started at a feasible basic solutionIllustrated on the Reddy Mikks problemOriginal LP formulationmaximizez= 5x1+ 4x2subject to6x1+ 4x2 24x1+ 2x2 6x1,x2 0 Standard LP formmaximizez= 5x1+ 4x2subject to6x1+ 4x2+x3= 24x1+ 2x2+x4= 6x1,x2,x3,x4 0 Operations Research Methods2 Lecture 6 Initial table vs Initial Simplex tableBasisx1x2x3x4 RHS Valuesz 5 4 0 0= 0?? 6 4 1 0= 24?? 1 2 0 1= 6 Basis:x3andx4 Basisx1x2x3x4 RHS Valuesz 5 4 0 0= 0x36 4 1 0= 24x41 2 0 1= 6 Initial table can be used as initial Simplex tableOperations Research Methods3 Lecture 6 Basis:x1andx4 Basisx1x2x3x4 RHS Valuesz 5 4 0 00x164 1 024x412 0 16 This table cannot be used as the initial Simplex table!

Lecture 6 Artificial Start: Two-phase method • Sometimes, it is not easy to find an initial feasible solution (i.e., to choose initial bases yielding a feasible point) • Two-phase method is used in such situations • In first phase, a feasibility problem associated with the LP is solved by a simplex method • In the second phase, the solution from the first phase is used to start

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  Methods, Simplex method, Simplex

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