Sensitivity analysis for specific sets of constraints on DoCplex

Question

I am working on DoCplex to run a large model with several variables and constraints. I used the following link from sensitivity analysis in python + Docplex to run the sensitivity analysis. In that example, there was a limited number of constraints and variables, which made it easy to interpret, but with a very large instance, the task becomes more tedious.

Therefore, I have a question if I name the set of constraints as mdl.add_constraint(nbbus40==nbbus30, 'samenumberofbuses'), will it be possible to run sensitivity analysis on the values on the right-hand side of a specific set of constraints? Instead of having the values for print(cpx.solution.sensitivity.rhs()) which will give me the values on all constraints, I would only have it for what I am focusing on.

Answer 1

You can filter the results you get from sensitivity.rhs :

See small example out of the zoo example again:

from docplex.mp.model import Model
from docplex.mp.relax_linear import LinearRelaxer

mdl = Model(name='buses')  
nbbus40 = mdl.integer_var(name='nbBus40')  
nbbus30 = mdl.integer_var(name='nbBus30')  
ctKids=mdl.add_constraint(nbbus40*40 + nbbus30*30 >= 300, 'kids')
ctKids2=mdl.add_constraint(nbbus40*40 + nbbus30*30 >= 290, 'kids2') 
mdl.minimize(nbbus40*500 + nbbus30*400)   
mdl.solve() 

lp = LinearRelaxer.make_relaxed_model(mdl)
m2 = lp.solve()

cpx = lp.get_engine().get_cplex()



print(cpx.solution.sensitivity.rhs())

rhs=cpx.solution.sensitivity.rhs()

names = cpx.linear_constraints.get_names()
print(names)

#Now we want the result only for constraint "kids"

indexConstraint=names.index("kids")

print("right info for the constraint ",rhs[indexConstraint])

which gives

[(290.0, 1e+20), (-1e+20, 300.0)]
['kids', 'kids2']
right info for the constraint  (290.0, 1e+20)