SUSPECT: Special Structure Detection for Pyomo¶
Release v2.1.3.
Note
SUSPECT requires Python 3. If you are using Python 2, please upgrade.
Installation¶
You can get SUSPECT from Pypi:
pip install cog-suspect
Quick Start¶
After we have constructed the model, we can pass it to
suspect.detect_special_structure() to obtain special
structure information
from suspect import detect_special_structure
import pyomo.environ as aml
model = aml.ConcreteModel()
model.x = aml.Var()
model.y = aml.Var()
model.obj = aml.Objective(expr=(model.y - model.x)**3)
model.c1 = aml.Constraint(expr=model.y - model.x >= 0)
info = detect_special_structure(model)
# try info.variables, info.objectives, and info.constraints
# in this case, objective is not detected as convex
print(info.objectives['obj'])
We can convert the Pyomo model to a _connected_ Pyomo model, where common sub-expressions are connected together in a Directed Acyclic Graph (DAG). With this extra information, SUSPECT will detect the objective as convex.
from suspect import create_connected_model
connected, _ = create_connected_model(model)
info = detect_special_structure(connected)
# now the objective is detected as convex!
print(info.objectives['obj'])
Quadratic Expression Support¶
SUSPECT extends Pyomo to include Quadratic expressions. If you use this feature, you should need to call the following function at the beginning of your script:
from suspect.pyomo import enable_standard_repn_for_quadratic_expression
enable_standard_repn_for_quadratic_expression()
Command Line Usage¶
SUSPECT comes with a command line tool to quickly inspect an optimization problem in the OSiL format:
$ model_summary.py -p /path/to/problem/instance.osil -s /path/to/problem/solution.p1.sol
This command will print a summary about the problem objective and constraints, for example:
$ model_summary.py -p /path/to/rsyn0805h.osil -s /path/to/rsyn0805h.p1.sol
INFO:root: Reading Problem
INFO:root: Converting DAG
INFO:root: Starting Special Structure Detection
INFO:root: Special Structure Detection Finished
{"bounds_obj_ok": true, "bounds_var_ok": true, "conscurvature": "convex", "name": "rsyn0805h", "nbinvars": 37, "ncons": 429, "nintvars": 0, "nvars": 308, "objcurvature": "linear", "objsense": "max", "objtype": "linear", "runtime": 0.21518850326538086, "status": "ok"}