22
votes
What is the purpose of libraries like Pyomo and Google OR tools?
Pyomo is an algebraic modeling language and allows users to easily represent optimization problems at a high-level (by defining variables, constraints, objective, etc.). Pyomo then provides interfaces ...
19
votes
What is the purpose of libraries like Pyomo and Google OR tools?
OR-Tools is a set of solver:
A very popular Routing Library built on top of a traditional constraint programming solver
An award winning ...
- 2,568
12
votes
Accepted
Warm start CPLEX using google or-tools
See answer on https://github.com/google/or-tools/issues/1444
This is not implemented.
I welcome pull requests.
You can have a look at the code in the Gurobi or Scip interface files.
- 2,568
10
votes
What is the purpose of libraries like Pyomo and Google OR tools?
Different solvers have their own interfaces (for example Cplex studio by IBM). You can use the specific syntax for those IDE or interfaces to input your model and then use the solver to solve it. ...
- 8,592
9
votes
Accepted
Maximize assigned tasks to each worker
Why quadratic?
just use a larger (linear) weight for tasks assigned to worker 1.
- 2,568
9
votes
Google - OR tools for workforce scheduling problems
In addition to the answer from @Mehdi... I've recently started to work with OR-tools and find it very nice for prototyping. The Python interface allowed me to produce a first version of my model ...
- 2,727
9
votes
Accepted
How to measure model quality in OR-Tools?
Time to solve (to proven optimality) is certainly a good choice. I don't know that I would be excited about number of conflicts.
You could look at the ratio of objective value on that problem ...
- 37.5k
9
votes
Accepted
Travelling salesman problem with given number of locations to visit
Thanks to @Laurent Perron for their answer - I've tried modifying the code as follows, and it appears to work fine:
...
- 271
9
votes
Accepted
How to Model Path Being Only Through Adjacent Cells
A standard approach for modeling a path from source $s$ to sink $t$ in a directed graph with node set $N$ and arc set $A$ is to let continuous variable $x_{ij} \ge 0$ represent the flow along the arc $...
- 29.8k
8
votes
Accepted
Precedence Constraint in OR-Tools
What you want is:
AddLessOrEqual(LinearExpr(starts[j]).AddConstant(durations[j]), starts[succ[j][s]])
You might also want to take a look at the examples (ending ...
- 1,404
8
votes
Google - OR tools for workforce scheduling problems
I used OR-tools for TSP and VRP. These are my observations:
1- It provides a good quality solution in reasonable time. However, it is not the optimal solution and in some cases you can find much ...
- 683
8
votes
Accepted
CP-SAT ortools - Is there any complete list of possible/available StringParameters for the CpSolver?
As many things in Google, OR-Tools uses Protocol Buffers to serialize data.
Here's a list of all .proto files in OR-Tools: https://github.com/google/or-tools/...
- 1,404
8
votes
Accepted
CP-SAT over CBC for MIP, is it worthwhile?
CP-SAT is a full fledged (non-mixed) integer programming solver (linear relaxation, presolve, cuts, branching heuristics). It is geared towards optimization, and is actually not very good at ...
- 2,568
8
votes
Accepted
Open source MILP solver for quick “good enough” solution
When I use CBC from time to time, it returns the best solution it has found even if it runs into the time limit. I guess, in your case, it has not even found a feasible solution.
I call it this way:
...
- 186
8
votes
How to add logical OR constraint in OR-Tools?
Introduce a binary variable $x_{d,s}$ and change the right hand side to $1+2x_{d,s}$.
- 29.8k
7
votes
Google - OR tools for workforce scheduling problems
Workforce scheduling describes many different problems.
The best technology for those is IMO CP-SAT (see the introduction, the reference manual in the CP-SAT sections and a set of recipes).
A ...
- 2,568
7
votes
Floating points in ORtools
In many of its solvers, OR-Tools only accept integers (see Laurent Perron's comment below).
Something like that:
...
- 521
7
votes
Accepted
Constraint Programming OR-Tools finding Matrix Combinations
You get the same result $2^{\operatorname{len}(y)}$ times because $y_i$ is not constrained.
You can see that by adding this to your callback:
...
- 1,404
7
votes
TSP problem: traveller does not visit all nodes - Google OR-tools
(already answered on S.O. )
You should have a look at Jobshop scheduling example with transitions
In particular, it maintains a graph of direct successor between tasks on the same machine.
- 2,568
7
votes
Accepted
Cumulative Constraint OR-Tools
If you look at OR-Tools: CumulativeConstraint, AddCumulative takes a variable as argument, so if it is constant, create a variable with a fixed domain.
It returns ...
- 2,568
7
votes
CP-SAT over CBC for MIP, is it worthwhile?
CP solvers can find optimal solutions (given enough time and memory). Essentially, like the "bound" part of branch-and-bound, each time you find a feasible solution you redefine feasibility to include ...
- 37.5k
7
votes
Open source MILP solver for quick “good enough” solution
Interestingly enough, one of the best source-open (!= open source) solvers is often overlooked: SCIP (download here); there is a Python interface (PySCIPOpt), too.
The parameter you need is ...
- 5,889
7
votes
find suboptimal solution, if no optimal solution exists?
If your linear program does not have an optimal solution one of three things might be the case:
The solver didn't find the optimal solution, even though it exists. This might be due to runtime or ...
- 2,401
7
votes
Travelling salesman problem variant without returning to the starting point
A TSP with a fixed starting point and no return to start, can be solved as an ordinary TSP with all the in-going arcs to the starting point having a cost of zero. That way the return to the starting ...
- 6,222
7
votes
Accepted
OR-Tools: Partial Solution ignored due to "unknown rate is too large"
Try:
SetSolverSpecificParametersAsString("heuristics/completesol/maxunknownrate = 0.9")
References:
SCIP params
SetSolverSpecificParametersAsString ...
- 1,404
7
votes
Accepted
Relevance of order of model construction in CP-SAT
This is a well know behavior of all MIP/CP solvers. Presolve and search are heavily heuristics based (to limit the complexity of the underlying algorithms), and thus are dependent on variables and ...
- 2,568
6
votes
How exactly does OptionalIntervalVar work in OR-Tools?
In the Python API there is a pretty good docstring of what an OptionalIntervalVar is:
An optional interval variable is a constraint, that is itself used in other
constraints like NoOverlap. This ...
- 1,404
6
votes
Incorrect solution for Vehicle Routing Problem in or-tools
I notice you are using FirstSolutionStrategy.Value.PATH_CHEAPEST_ARC. If this name does what it suggests, then it's probably a greedy strategy that chooses between ...
- 295
6
votes
Adding a hard and soft upper bound constraint of number of locations to visit (VRP)
Crossposted from: Stack Overflow
The idea is to create another dimension ('visit') that is incremented by 1 on each visit.
Then use SetCumulVarSoftUpperBound on ...
- 2,568
6
votes
Priority List Constraint
If I understand your problem correctly, you have a standard CVRP and a second (soft) objective.
You are therefore in the wonderful world of multi-objective optimization.
Typically what you do is ...
- 2,401
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