cplex cpo optimisation (getting value of variables other than decision varibales from model)

Question

I am using cplex cpo model for optimisation problem in python. I am beginner and I am learning. I am facing an issue which is given below.

I have the following binary decision variables:

model.binary_var(name='gamma1')
model.binary_var(name='gamma2')
model.binary_var(name='gamma3')
model.binary_var(name='gamma4')`

I have another variable defined as:

d = 
5gamma1 + 13gamma2 + 17gamma3 + 45gamma4 /  sum(gamma1 +gamma2+gamma3)`

objective function = minmization problem depending on decision and many other values

When I solve the optmization problem, I can get the values of gamma by following

model.add(model.minimize(objectiveFunction))
solution = model.solve( )
all_variables = model.get_all_variables()

# Iterate over all variables
print("All Variables:")
for var in all_variables:
    print(var.get_name(), "-", var.get_type(), "Variable", solution.get_value(var), "solution"

But I am unable to get value of "d ". Is there a way I can get this value from model? (not to recalculate like getting optimized gamma value and calling a function to calculate d)

I've tried

solution.get_var_solution(d)
solution.get_value(d)

Answer 1

You can use kpi for that.

See example at https://github.com/AlexFleischerParis/zoodocplex/blob/master/zookpicpo.py

from docplex.cp.model import CpoModel

mdl = CpoModel(name='buses')
nbbus40 = mdl.integer_var(0,1000,name='nbBus40')
nbbus30 = mdl.integer_var(0,1000,name='nbBus30')

nbbus=nbbus40+nbbus30
mdl.add_kpi(nbbus,"nbbus")

mdl.add(nbbus40*40 + nbbus30*30 >= 300)
mdl.minimize(nbbus40*500 + nbbus30*400)

msol=mdl.solve()

print(msol[nbbus40]," buses 40 seats")
print(msol[nbbus30]," buses 30 seats")

print("nbbus = ",msol["nbbus"])