Could not locate Xpress

[Roland Vincze]

Hi!

Is the Xpress plugin fully functional? I read in an earlier post from 2014 it is not ready yet.

If yes, how is it locating the xpress executable/dll? I installed the student version from the official xpress site, but pyomo does not seem to find it:

WARNING: "[base]\site-packages\pyomo\solvers\plugins\solvers\XPRESS.py", 98, executable

Could not locate the 'optimizer' executable, which is required for solver xpress

Xpress created the following system variables:

CLASSPATH=%XPRESSDIR%\lib\xprs.jar;%XPRESSDIR%\lib\xprb.jar;%XPRESSDIR%\lib\xprm.jar;
INCLUDE=%XPRESSDIR%\include;
LIB=%XPRESSDIR%\lib;
XPRESSDIR=C:\Programs\xpressmp

(The first three of these are not working, since the 'lib' directory is not present.)

[Gabriel Hackebeil]

You can use Xpress through the ASL interface (solver=“amplxpress”)

https://groups.google.com/forum/#!searchin/pyomo-forum/Error$20when$20trying$20to$20use$20xpress/pyomo-forum/DSlLB5jeJWk/BoqNIkxPBAAJ

Gabe

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[Roland Vincze]

Thanks for the quick reply!

Now, however, I get the SolverFactory's UnknownSolver error message:

RuntimeError: Attempting to use an unavailable solver.

The SolverFactory was unable to create the solver "amplxpress"

and returned an UnknownSolver object.  This error is raised at the point

where the UnknownSolver object was used as if it were valid (by calling

method "solve").

The original solver was created with the following parameters:

type: amplxpress

_args: ()

options: {}

[Gabriel Hackebeil]

That means you don’t have the amplxpress executable or it is not in your PATH. If it is not in the Xpress bin directory, it means it is probably a separate download.

Gabe

[Roland Vincze]

Does Pyomo use an executable or dlls? I have only dll files in folder xpressmp\bin, and an IDE executable in folder xpressmp.

[Gabriel Hackebeil]

Pyomo uses executables. Some solvers like Cplex and Gurobi have a Python interface as well.

Gabe

[Roland Vincze]

It looks like the student version does not have the functionality to connect it with Pyomo in any way.

However, I have an ampl package (ampl exec + solver exes and dlls) from my university, with university license. It has xpress.exe, I checked and the license is valid. The path of this folder is the first in the PATH variable. I still get the same errors as above, when trying to call "xpress" or "amplxpress" with SolverFactory.

[Gabriel Hackebeil]

We don’t have a functional solver plugin for the xpress executable, just amplxpress.

Gabe

[Roland Vincze]

I see, but what actually is amplxpress? I can't find any info about it. If I have AMPL and a functioning xpress solver for it, I would assume I have amplxpress.

[Gabriel Hackebeil]

Good question. I have only seen it on a computer that belonged to someone else, and it was a linux machine. I had just assumed it came with Xpress, but maybe there is something we should be able to do with the DLLs on Windows. Any ideas? I don’t have much experience with this kind of thing on Windows.

Gabe

[Gabriel Hackebeil]

Does the xpress executable take a “-AMPL” option? It might be that they are the same executable in your version (or just on Windows). You can try something like the following:

model.write(“test.nl”)

os.system(“xpress test.nl -AMPL”)

Gabe

[Roland Vincze]

Okay :D well, I am out of ideas, that's why I am writing here :)

But I actually need this only for a brief double-checking, since Gurobi gives me weird results. I have Knitro, too, and I was able to make it work. However, it does not make any logfile, which I would need. I searched but found only a tertiary logging option (0-console, 1-logfile, 2-both), but it does not make any logfile no matter what. I could not find an option for changing the logfile, either.

Edit: I just saw your answer. For that, xpress only gives the following answer:

XPRESS 28.01: xpress: jacdim: got M = 0, N = 0, NO = 0

[Gabriel Hackebeil]

Edit: I just saw your answer. For that, xpress only gives the following answer:

XPRESS 28.01: xpress: jacdim: got M = 0, N = 0, NO = 0

Well that means xpress is amplxpress, because that is ASL output. The following should work:

SolverFactory(“asl”, executable=“xpress”)

Let me know if it does not.

I’ll try to look into what is going on with Xpress on different systems when I find some time in the next month.

Gabe

[Roland Vincze]

I get

WARNING: "[base]\site-packages\pyomo\solvers\plugins\solvers\ASL.py", 73, executable

No solver option specified for ASL solver interface

Traceback (most recent call last):

  File "C:\Users\Rolf\git\cvar\src\tests\Solvers.py", line 25, in <module>

    result = opt.solve(model)

  File "C:\Programs\Anaconda2\lib\site-packages\pyomo\opt\base\solvers.py", line 499, in solve

    self.available(exception_flag=True)

  File "C:\Programs\Anaconda2\lib\site-packages\pyomo\opt\solver\shellcmd.py", line 52, in available

    raise ApplicationError(msg % self.name)

pyutilib.common._exceptions.ApplicationError: No executable found for solver 'asl'

even if I put the full path "c:\...\xpress.exe". Strange thing is, it does not work with other solvers this way.

If we can't resolve this issue, could you please tell me how to make Knitro to write a log file?

[Gabriel Hackebeil]

Given the line numbers in that stack trace, it looks like you are on an older version of Pyomo that probably isn’t aware of the “executable” keyword. It will most likely work if you upgrade to the latest release. If you installed with pip, then you should be able to update by running

pip install -U Pyomo

Gabe

P.S. Knitro is another Frontline solver that is not easy to get a license to test with, so I can’t really provide much help there.

[Roland Vincze]

Whoa, it works! And the logging works, too. Thank you!

One small thing: after I updated pyomo, I get the following error every time if I run python or even conda (I'm using Anaconda2):

Error processing line 2 of C:\Programs\Anaconda2\lib\site-packages\Pyomo-4.3.11377-py2.7-nspkg.pth:

  Traceback (most recent call last):

    File "C:\Programs\Anaconda2\lib\site.py", line 152, in addpackage

      exec line

    File "<string>", line 1, in <module>

  KeyError: 'pyomo'

Remainder of file ignored

I have two rows in the .pth file mentioned above:

import sys, types, os;p = os.path.join(sys._getframe(1).f_locals['sitedir'], *('pyomo',));ie = os.path.exists(os.path.join(p,'__init__.py'));m = not ie and sys.modules.setdefault('pyomo', types.ModuleType('pyomo'));mp = (m or []) and m.__dict__.setdefault('__path__',[]);(p not in mp) and mp.append(p)

import sys, types, os;p = os.path.join(sys._getframe(1).f_locals['sitedir'], *('pyomo', 'data'));ie = os.path.exists(os.path.join(p,'__init__.py'));m = not ie and sys.modules.setdefault('pyomo.data', types.ModuleType('pyomo.data'));mp = (m or []) and m.__dict__.setdefault('__path__',[]);(p not in mp) and mp.append(p);m and setattr(sys.modules['pyomo'], 'data', m)

If I comment out the second one, everything is working. Should I worry?

[Gabriel Hackebeil]

It looks like maybe you had previous installed Pyomo using the Windows installer. Otherwise, I don’t know why you would have any references to pyomo.data, etc. If might be best clean your installation of anything pyomo / pyutilib related by downloading pyomo_uninstall.py and then running

pip uninstall pyomo pyutilib

python pyomo_uninstall.py

Then reinstall pyomo using pip

pip install pyomo

Gabe

On May 18, 2016, at 10:02 AM, Roland Vincze <roli....@gmail.com> wrote:

Whoa, it works! And the logging works, too. Thank you!

One small thing: after I updated pyomo, I get the following error every time if I run python or even conda (I'm using Anaconda2):

Error processing line 2 of c:\programs\anaconda2\lib\site-packages\Pyomo-4.3.11377-py2.7-nspkg.pth:

  Traceback (most recent call last):

    File "c:\programs\anaconda2\lib\site.py", line 152, in addpackage

      exec line

    File "<string>", line 1, in <module>

  KeyError: 'pyomo'

[Roland Vincze]

Yes, I messed with pip and conda installs. I will try what you wrote. Thank you for all the help!

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[Gabriel Hackebeil]

No problem.

Gabe