m.getAttr('X', x) gives warning

Answered

Simon Hoof

November 17, 2022 07:42 Edited

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I'm solving the following MWE: 

import gurobipy as gp
from gurobipy import GRB

# Parameter
N = (1, 2)
M = (1, 2)
c = {'x': {1:  2, 2:  1},
     'y': {1:  3, 2: -1},}

A = {'x': {(1, 1):  1, (1, 2):  2,
           (2, 1): -1, (2, 2): -1,},
     'y': {(1, 1):  0, (1, 2):  1,
           (2, 1):  2, (2, 2): -1,}}

b = {1: 4,
     2: 2}

# Create a new model
m = gp.Model()

# Create variables
x = m.addVars(N, vtype=GRB.CONTINUOUS, name='x')
y = m.addVars(N, vtype=GRB.CONTINUOUS, name='y')

# Set objective
m.setObjective(sum(x[i] * c['x'][i] + y[i] * c['y'][i] for i in N), GRB.MAXIMIZE)

# Add constraints
for j in M:
    m.addConstr(sum(A['x'][j, i] * x[i] + A['y'][j, i] * y[i] for i in N) <= b[j],
                name=f'Const[{j}]')

# Optimize model
m.optimize()

# Solution
x_sol = m.getAttr('X', x)
y_sol = m.getAttr('X', y)

It works and \(\texttt{x_sol}\) and \(\texttt{y_sol}\) contain the correct solutions for the respective variable. But my editor PyCharm tells me that there is a problem, namely that \(\texttt{m.getAttr('X', x)}\) and \(\texttt{m.getAttr('X', y)}\) contain and "Unexpected argument" and the fix  would be to drop \(\texttt{x}\) and \(\texttt{y}\), respectively. If I would do that the returned solution is a list and cannot distinguish between the \(\texttt{x}\)s and \(\texttt{y}\)s.

I was wondering whether this is a PyCharm or Gurobi issue and if it was a Gurobi issue, what would be the proper way to call the solution.

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  Matthias Miltenberger

  • Gurobi Staff

  November 17, 2022 10:22 Edited

  I don't see a warning with VSCode. Maybe you should install Gurobi/gurobipy-stubs (github.com) to get the correct type hints?

  Providing a set of constraints or variables to the getAttr() method is certainly possible and should not trigger a warning.

  Cheers,
  Matthias

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