GurobiError: Invalid argument to LinExpr multiplication

[Camille]

I am using Spyder (Python 2.7). 

I am getting the following error: GurobiError: Invalid argument to LinExpr multiplication

I am still quite new to programming in general. Is there someone who can explain me what I am doing wrong ? 

Thanks,

Camille

from gurobipy import *

kostenInputFile = open("INFLAKOSTEN.txt");

scoresInputFile = open("OPBRENGST.txt");

kostenArray = kostenInputFile.read().split();

scoresArray = scoresInputFile.read().split();

print "Kosten::"

print str(kostenArray)

print "Scores::"

print str(scoresArray)

 

m = Model("mip1")

 

projectEnabledVars = [];

for i in xrange(0, 600):

    projectEnabledVars.append(m.addVar(vtype=GRB.BINARY, name="X_"+str(i)))

m.update();

 

objective = 0;

for i in xrange(0, len(scoresArray)):

    objective+=projectEnabledVars[i]*scoresArray[i]

m.setObjective(objective, GRB.MAXIMIZE)

m.update();

 

constraint = 0;

for i in xrange(0, len(scoresArray)):

    constraint += projectEnabledVars[i] * kostenArray[i]

m.addConstr(constraint <= 30000000, "Budget")

m.update();

 

m.optimize();

 

print('Obj: %g' % m.objVal)

for v in m.getVars():

    print('%s %g' % (v.varName, v.x))

[Kostja Siefen]

Hi Camille,

Make sure you convert your input data to a proper data type (e.g. convert values of kostenArray and scoresArray to float). 

To create linear expressions (objective / left-hand side of constraints) you can use the quicksum() function, e.g.

objective = quicksum([ projectEnabledVars[i] * scoresArray[i] for i in xrange(len(scoresArray)) ])

m.setObjective(objective, GRB.MAXIMIZE)

Best wishes,

Kostja