CPLEX constraint with absolute values in Python

Question

I'm trying to create two constraints in CPLEX (using python): one using the variable X, and the other using abs(X). Something like:

x > 0
abs(x) > 0

Should I create a new constraint Y that receives the value of abs(X), or is it possible to include abs(X) directly in "linear_constraints.add"?

The code below is not functional:

from cplex import Cplex, SparsePair

constraints = [{'abs(X)': 1},{'X': 1}]
exprs = [SparsePair(ind=list(constr.keys()), val=list(constr.values())) for constr in constraints]

model.linear_constraints.add(lin_expr=exprs, names=['constr_1','constr_2'])

Any ideas? Thank you.

Alex Fleischer · Accepted Answer · 2021-09-17 07:48:54Z

2

tiny example with docplex python API

from docplex.mp.model import Model

mdl = Model(name='buses')
nbbus40 = mdl.integer_var(name='nbBus40')
nbbus30 = mdl.integer_var(name='nbBus30')
mdl.add_constraint(nbbus40*40 + nbbus30*30 >= 300, 'kids')

#absolute value of nbBus40 - nbBus30
mdl.add_constraint(mdl.abs(nbbus40-nbbus30)<=2)

mdl.minimize(nbbus40*500 + nbbus30*400)

mdl.solve(log_output=True,)



for v in mdl.iter_integer_vars():
    print(v," = ",v.solution_value)

answered Sep 17, 2021 at 7:48

Alex Fleischer

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