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I'm running SoPlex from the command line to solve some linear programming problems. I'd like to get the basis of the solution, so I use the --writebas flag. However, I can't find a description of the file format of the basis output. For example, running soplex test.lp --writebas=basis on

\ test.lp
Maximize
 obj: x1 + 2 x2 + 3 x3 + x4
Subject To
 c1: - x1 + x2 + x3 + 10 x4 <= 20
 c2: x1 - 3 x2 + x3 <= 30
 c3: x2 - 3.5 x4 = 0
Bounds
 0 <= x1 <= 40
 2 <= x4 <= 3
General
 x4
End

gives the basis file:

NAME  soplex.bas
 UL x1
 XU x2             c1
 XU x3             c2
 XL x4             c3
ENDATA

What does this mean?

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1 Answer 1

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This is a standard MPS Basis file. Its format goes back to ancient Roman times. Here is a good description: http://lpsolve.sourceforge.net/5.5/bas-format.htm.

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  • $\begingroup$ ...Ancient roman times... $\endgroup$
    – Milind R
    Commented Mar 15 at 9:59

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