Using NEOS solvers in a script

[Bethany Nicholson]

Is there a way to call NEOS solvers from a python script? I'm guessing it's just a matter of specifying the right options for the SolverFactory but I can't figure out what they are.

Bethany

[Watson, Jean-Paul]

There is a NEOS-specific solver manager, but that is about all I know. For example, if you run from the pyomo command line (which I realize you aren’t), you say something like “pyomo —solver-manager=neos —solver=cplex …”. 

Hopefully someone else knows more…

jpw

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[William Hart]

I'm sure I know, but I've forgotten.  Let me try to build a simple example ...

[Daniel Friedrich]

I was just looking into this and found the solution in the documentation; see code snippet. 

Cheers,

Daniel

Code snippet:

instance = model.create('test_pyomo.dat')

opt = SolverFactory("cbc")

solver_manager = SolverManagerFactory('neos')

results = solver_manager.solve(instance, opt=opt)

results.write()

[Bill Hart]

Thanks, Daniel!

[mchehreg]

Hi all, 

When I use Neos server to solve my MILP problem with cplex, as it's explained in this thread, I get the following error:

===============================

  results = solver_manager.solve(instance, opt=opt)

  File "C:\Anaconda\envs\env_pyomo\lib\site-packages\pyomo\opt\parallel\async_solver.py", line 33, in solve

    return self.execute(*args, **kwds)

  File "C:\Anaconda\envs\env_pyomo\lib\site-packages\pyomo\opt\parallel\manager.py", line 91, in execute

    results = self.wait_for(ah)

  File "C:\Anaconda\envs\env_pyomo\lib\site-packages\pyomo\opt\parallel\manager.py", line 156, in wait_for

    tmp = self.wait_any()

  File "C:\Anaconda\envs\env_pyomo\lib\site-packages\pyomo\opt\parallel\manager.py", line 145, in wait_any

    ah = self._perform_wait_any()

  File "C:\Anaconda\envs\env_pyomo\lib\site-packages\pyomo\neos\plugins\kestrel_plugin.py", line 122, in _perform_wait_any

    solver_results = self._opt.process_output(rc)

  File "C:\Anaconda\envs\env_pyomo\lib\site-packages\pyomo\opt\solver\shellcmd.py", line 228, in process_output

    results = self.results_reader(self.results_file, res=results, suffixes=self.suffixes)

  File "C:\Anaconda\envs\env_pyomo\lib\site-packages\pyomo\opt\plugins\sol.py", line 78, in __call__

    raise ValueError(msg)

ValueError: Error reading "c:\users\mc\appdata\local\temp\tmp2x9jbw.neos.sol": no Options line found.

SOL File Output:

ERROR: An error occured with your submission.

=============

In my log file, I get the following message: 

===============================

Job 3771867 submitted to NEOS, password='OvlqHczQ'

Check the following URL for progress report :

http://www-neos.mcs.anl.gov/neos/cgi-bin/nph-neos-solver.cgi?admin=results&jobnumber=3771867&pass=OvlqHczQ

Job 3771867 dispatched

password: OvlqHczQ

---------- Begin Solver Output -----------

Job submitted to NEOS HTCondor pool.

=============

and when I check neos website with the given credentials to view job results, I get:

================================

Job 3771867 has finished.
Job 3771867 dispatched
password: OvlqHczQ
---------- Begin Solver Output -----------
Job submitted to NEOS HTCondor pool.

=============

Neos takes more than 30sec to solve the problem when I upload the LP model directly via its web interface. Any idea how I can fix this to get the result using pyomo's SolverManagerFactory interface?

Thanks a lot.