I do not understand how cloned models in docplex can be modified.
from docplex.mp.model import Model
mdl_1 = Model('Model 1')
x = mdl_1.integer_var(0, 10, 'x')
mdl_1.add_constraint( x <= 10)
mdl_1.maximize(x)
mdl_1.solve()
#now clone
mdl_2 = mdl_1.clone(new_name='Model 2')
mdl_2.add_constraint( x <= 9) # throws (x <= 9) is not in model 'Model 2'
The error makes sense, as x was created for Model 1, but how do I get the 'cloned x' to modify Model 2?
Variable belong to one model. You can retrieve a variable either via its name (assuming it is unique) or its index.
Answer 1: use variable name
x_2 = mdl_2.get_var_by_name('x')
mdl_2.add_constraint( x_2 <= 9) # throws (x <= 9) is not in model 'Model 2'
print(mdl_2.lp_string)
Answer 2: use the variable index
x_2 = mdl_2.get_var_by_index(x.index)
mdl_2.add_constraint( x_2 <= 9) # throws (x <= 9) is not in model 'Model 2'
print(mdl_2.lp_string)
However, the two solutions above add one extra constraint, it would be better to edit the lhs. This is done by retrieveing the constraint's clone via its index:
Answer 3: use the constraint index, edit rhs
c_2 = mdl_2.get_constraint_by_index(c1.index)
c_2.rhs = 9 # modify the rhs of the cloned constraint , in place
print(mdl_2.lp_string)
In this last approach, the cloned model has only one constraint, not two.
output:
\Problem name: Model 2
Maximize
obj: x
Subject To
ct_x_10: x <= 9
Bounds
x <= 10
Generals
x
End