Pyomo and ipopt - execution from Python

[Michele Pratusevich]

Hi all -

I am new to optimization and found Pyomo to be a good integration into my workflow. I am trying to solve a quadratic program with ipopt (I am no longer a student so I can't get licenses for the fancy solvers out there). 

I have defined a simple ConcreteModel:

model = ConcreteModel().....

And then have attempted to call the ipopt solver from Python, as follows:

ipopt_solver = pyomo.opt.solvers.SolverFactory('ipopt')

ipopt_solver.solve(model)

But the solver doesn't give me a solution back. However, when I use command-line pyomo: 

pyomo solve --solver=ipopt model_script.py

I get a solution back. I would really like to be able to call the solver directly from Python but can't seem to be able to. Any ideas?

Michele

[Michael Bynum]

Are you getting an error? If so, can you post the stack trace?

If you are not getting an error, are you saving the results? For example, you could do:

results = ipopt_solver.solve(model, tee=True)
model.load(results)
model.pprint()

The tee=True will show ipopt output.

Michael

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[Gabe Hackebeil]

In older versions of Pyomo, the solution was found in the return value from "ipopt_solver.solve(model)". In more recent versions the solution is loaded into the model automatically. The return value still contains other useful information about the solver exit status and related messages. Try printing it to get an idea of the information it contains. Sometimes it is necessary for scripts to check this information when dealing with models that are potentially infeasible.

Gabe

> On Oct 25, 2015, at 8:01 PM, Michele Pratusevich <michelepr...@gmail.com> wrote:
>
> ipopt_solver.solve(model)