No executable found for solver ipopt on Ubuntu 20.04

[wigging]

I'm trying to install IDAES on the following system where Python is installed via Miniconda.

Ubuntu 20.04.5 LTS x86_64
Linux 5.4.0-125-generic
Bash 5.0.17
Intel Xeon E5-2680 v3 (20) @ 2.499GHz
Python 3.10.4

Following the steps in the IDAES documentation for Linux, I ran the following commands and didn't notice any errors during the installation.

sudo apt-get install libgfortran5 libgomp1 liblapack3 libblas3

conda create --name idaes python

conda activate idaes

conda install --yes -c IDAES-PSE -c conda-forge idaes-pse

idaes get-extensions

Example Python script to run.

from pyomo.environ import Objective, Constraint, value, SolverFactory
from pyomo.environ import ConcreteModel, Var

model = ConcreteModel()
model.x = Var()
model.y = Var()

model.obj = Objective(expr=model.x**2 + model.y**2)

model.con = Constraint(expr=model.x + model.y == 1)

status = SolverFactory('ipopt').solve(model, tee=True)  # tee=True shows the solver log

print('x =', value(model.x))
print('y =', value(model.y))
print('obj =', value(model.obj))

Errors reported from running the example are shown below.

WARNING: Could not locate the 'ipopt' executable, which is required for solver
    ipopt
Traceback (most recent call last):
  File "/home/cades/idaes-examples/example1.py", line 20, in <module>
    status = SolverFactory('ipopt').solve(model, tee=True)  # tee=True shows the solver log
  File "/home/cades/miniconda3/envs/idaes/lib/python3.10/site-packages/pyomo/opt/base/solvers.py", line 513, in solve
    self.available(exception_flag=True)
  File "/home/cades/miniconda3/envs/idaes/lib/python3.10/site-packages/pyomo/opt/solver/shellcmd.py", line 129, in available
    raise ApplicationError(msg % self.name)
pyomo.common.errors.ApplicationError: No executable found for solver 'ipopt'

It looks like the ipopt solver was not installed. Is there another step I'm supposed to do for Linux?

[lbianchi-lbl]

Hi @wigging, can you try using from idaes.core.solvers import get_solver instead of SolverFactory?

[wigging]

I tried the following but get an import error.

from idaes.core.solvers import get_solver

solver = get_solver()
solver.solve(model, tee=True)

Here's the error.

Traceback (most recent call last):
  File "/home/cades/idaes-examples/example1.py", line 12, in <module>
    from idaes.core.solvers import get_solver
ImportError: cannot import name 'get_solver' from 'idaes.core.solvers' (/home/cades/miniconda3/envs/idaes/lib/python3.10/site-packages/idaes/core/solvers/__init__.py)

[wigging]

I think this approach requires watertap to be installed. I'm just trying to run IDAES examples right now and have not installed watertap yet.

[andrewlee94]

I suspect the problem is the version of IDAES. My guess is that without specifying a version when you did the conda install, you got the last stable version of IDAES (v1.13). We have changed the API since then in preparation for v2.0, and one of those was moving get_solver.

[lbianchi-lbl]

@wigging, thanks for trying that. I think this might be due to the aforementioned breaking changes on the IDAES side: I used the current import path, which is different from the legacy import path that's available to the version of IDAES with which WaterTAP is (as of now) compatible. I understand that these issues can be confusing in general, and even more so for someone just joining the project during this "pardon our dust" stage. Our current priority is to make the codebase compatible with IDAES 2.0 as soon as possible.

[andrewlee94]

@wigging The issue is that the IDAES IPOPT solver is only available through IDAES (for licensing reasons). You can also fix the issue by doing import idaes at the beginingg of your script.

[wigging]

@lbianchi-lbl Yes, I'm aware if running things with __main__ but left that out to shorten the example code.

@andrewlee94 I've never heard of this ipopt solver. Where do I get more information about it?

[andrewlee94]

I am referring to the pre-compiled version of IPOPT you get from the idaes get-extensions command.

[wigging]

@andrewlee94 Doing import idaes works. Is this explained somewhere in the docs that you need to import idaes?

[andrewlee94]

I think it is, but it is buried somewhere and easy to miss.

[wigging]

The Using Solvers Without IDAES section in the docs discusses setting the paths with import idaes.
https://idaes-pse.readthedocs.io/en/stable/tutorials/getting_started/binaries.html