multiplication of CyLPExpr by constant not commutative

[sdementen]

When multiplying by a constant before or after a variable.sum() I get a wrong / good answer

from cylp.cy.CyClpSimplex import CyClpSimplex

s = CyClpSimplex()
x = s.addVariable("x", 2)
y = s.addVariable("y", 2)
s += y >= 0
s += y.sum() - x.sum() * 3 <= -1  # ==> gives wrong solution x=[0,1]
# s += y.sum() - 3 * x.sum() <= -1  # ==> gives correct solution x=[0,0.3333]
s.objective = x.sum()
s.primal()

The two expressions y.sum() - x.sum() * 3 <= -1 and y.sum() - 3 * x.sum() <= -1 should represent the same constraint and give the same results but only the second gives the correct model.

[rsemenoff]

I believe this is a documented limitation.  On Friday, January 28, 2022, 05:08:03 AM PST, sdementen ***@***.***> wrote: When multiplying by a constant before or after a variable.sum() I get a wrong / good answer from cylp.cy.CyClpSimplex import CyClpSimplex s = CyClpSimplex() x = s.addVariable("x", 2) y = s.addVariable("y", 2) s += y >= 0 s += y.sum() - x.sum() * 3 <= -1 # ==> gives wrong solution x=[0,1] # s += y.sum() - 3 * x.sum() <= -1 # ==> gives correct solution x=[0,0.3333] s.objective = x.sum() s.primal() The two expressions y.sum() - x.sum() * 3 <= -1 and y.sum() - 3 * x.sum() <= -1 should represent the same constraint and give the same results but only the second gives the correct model. — Reply to this email directly, view it on GitHub, or unsubscribe. Triage notifications on the go with GitHub Mobile for iOS or Android. You are receiving this because you are subscribed to this thread.Message ID: ***@***.***>