I have developed a linear program and implemented it in Python via docplex. I would like to know how one can print the dual model using docplex? I have seen similar posts for other programming languages, but I was unable to find relevant discussions for docplex.
I would use cplex command line from python through an external call.
If I use the zoo example
import os
from docplex.mp.model import Model
mdl = Model(name='buses')
nbbus40 = mdl.continuous_var(name='nbBus40')
nbbus30 = mdl.continuous_var(name='nbBus30')
mdl.add_constraint(nbbus40*40 + nbbus30*30 >= 300, 'kids')
mdl.minimize(nbbus40*500 + nbbus30*400)
mdl.solve(log_output=True,)
mdl.export("buses.lp")
for v in mdl.iter_continuous_vars():
print(v," = ",v.solution_value)
os.system("cplex -c \"read buses.lp\" \"write buses.dua\"")
then in buses.dua I get
NAME buses.lp.dual
ROWS
N rhs
G nbBus40
G nbBus30
COLUMNS
kids rhs -300
kids nbBus40 -40
kids nbBus30 -30
RHS
obj nbBus40 -500
obj nbBus30 -400
ENDATA
which gives in lp format
Minimize
rhs: - 300 kids
Subject To
nbBus40: - 40 kids >= -500
nbBus30: - 30 kids >= -400
End