0

I'm trying to understand how to use NEOS Server for SCIP. I already read the tutorial about the CPLEX LP file format. But still I'm not able to get any results.

Let's take the example provided in that tutorial:

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

In what format (file extension) do I have to save that? I tried .MPS and uploaded it using the 1st button (Enter the complete path to the MPS format data file). But I got:

error reading file <sample.mps>
SCIP> file <sample.osil> not found
SCIP> limits/time = 36000
SCIP> loaded parameter file <scip.set>
SCIP> 
no problem exists

SCIP> 
written solution information to file <results1>

SCIP> 
written statistics to file <results2>

SCIP> solution status: unknown
no solution available
SCIP Status        : initialization
Original Problem   : no problem exists.
Evgenij Reznik
  • 17,916
  • 39
  • 104
  • 181

1 Answers1

3

If you write a file in CPLEX LP file format, you should upload it using the second button, which is for this format. I tried it and it runs smoothly. The file extension should be ".lp", but the NEOS server seems to automatically rename it to the correct ending.

The MPS format (see, e.g., http://lpsolve.sourceforge.net/5.5/mps-format.htm) is an alternative, but by far not as human-readable as the LP format.

If you want to model more complex problems, you should have a look at mathematical modeling languages. The NEOS server allows to also read in ZIMPL files (see zimpl.zib.de), which is the modeling language shipped together with SCIP in the SCIP Optimization Suite. But also GAMS, AMPL and OSIL are available.

Gerald
  • 696
  • 3
  • 7