Pyomo: Access Solution From Python Code

Question

I have a linear integer programme I want to solve. I installed solver glpk (thanks to this answer) and pyomo. I wrote code like this:

from pyomo.environ impo         


        

Answer 1

Here's a modified version of your script that illustrates two different ways of printing variable values: (1) by explicitly referencing each variable and (2) by iterating over all variables in the model.

# Pyomo v4.4.1
# Python 2.7
from pyomo.environ import *
from pyomo.opt import SolverFactory

a = 370
b = 420
c = 4

model             = ConcreteModel()
model.x           = Var([1,2], domain=Binary)
model.y           = Var([1,2], domain=Binary)
model.Objective   = Objective(expr = a * model.x[1] + b * model.x[2] + (a-b)*model.y[1] + (a+b)*model.y[2], sense=maximize)
model.Constraint1 = Constraint(expr = model.x[1] + model.x[2] + model.y[1] + model.y[2] <= c)

opt = SolverFactory('glpk')

results = opt.solve(model)

#
# Print values for each variable explicitly
#
print("Print values for each variable explicitly")
for i in model.x:
  print str(model.x[i]), model.x[i].value
for i in model.y:
  print str(model.y[i]), model.y[i].value
print("")

#
# Print values for all variables
#
print("Print values for all variables")
for v in model.component_data_objects(Var):
  print str(v), v.value

Here's the output generated:

Print values for each variable explicitly
x[1] 1.0
x[2] 1.0
y[1] 0.0
y[2] 1.0

Print values for all variables
x[1] 1.0
x[2] 1.0
y[1] 0.0
y[2] 1.0