How to print the value of Vars within a solution?
Answered
my objective function is:
m.setObjective(x.prod(cost) + y.prod(trip))
now when I finish m.optimize(),
I want to get the value of term x.prod(cost),
but when I print that, the result just shows an equation, rather than the value number.
How can I change the code?
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x is a variable in my model
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Hi Runqing,
tupledict.prod() returns a LinExpr object. You can use the LinExpr.getValue() method to retrieve the value of a linear expression evaluated at the current solution. In your case, you should be able to print the desired value using
x.prod(cost).getValue()
Thanks,
Eli
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Thank you very much for you help!
I have solved this problem by your solution.
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I just come up with another question:
I wanna print the sum of these four items, but it is linear expression again, and getValue is not available because they are list.
y_flow.select('*', '*', 1)
y_flow.select('*', '*', 2)
y_flow.select('*', '*', 3)
y_flow.select('*', '*', 4)How can I solve this one?
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Hello,
Will .getValue() work on something like this?
\[\max\pi\]
\[\sum (1 - y_i) \,\leq\,k\]
\[A \nu = b\]
\[l_{i} \hat{y}_{i}^{R} \, \leq v_{i} \, \leq u_{i} \hat{y}_{i}^{R}\]
\[\pi\,\leq f_{0}(\tilde\nu^R)\,-\,M\sum\limits_{i \in I_{R}^{+}}(1 - y_{i})\tilde\nu_{i}^R\,+\,M\sum\limits_{i \in I_{R}^{-}}(1-y_{i})\tilde\nu_{i}^{R}\]I am interested in getting the values of v and pi so I can add some lazy cuts
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Hi Runqing,
Although y_flow.select('*', '*', 1) is not a linear expression object, y_flow.sum('*', '*', 1) is. Thus, you could use the getValue() method of this expression instead. More information on the tupledict.sum() method can be found here.
Alternatively, you could sum the variable values using the X attribute:
sum(y.X for y in y_flow.select('*', '*', 1))Jose, you can query the individual values of variables with the X attribute. To do this inside of a callback when a new feasible MIP solution is found, you can use Model.cbGetSolution() in the MIPSOL callback. For code examples of this, I recommend looking at callback.py and tsp.py from the examples library.
Thanks,
Eli
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Hi Eli,
Your suggestion works well. Thank you very much!
Runqing
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