Custom cost function

[igor r]

Hi,

Is it possible to set a custom cost function?

If not which ways can it be adjusted?

I found only one example of this with SetGlobalSpanCostCoefficient

[Mizux Seiha]

You can't have a custom cost function, BUT the cost function can integrate:

- [mandatory] The sum of all arc cost used (used by any initial first strategy)

  ref: https://github.com/google/or-tools/blob/b37d9c786b69128f3505f15beca09e89bf078a89/ortools/constraint_solver/routing.h#L901-L906
- [optional] The span cost of any dimension (e.d. one coefficient per vehicle, default 0)

- [optional] The global span cost of any dimension (e.d. one coefficient per dimension, default 0)
- [optional] A vehicle fixed cost (e.d. one cost per vehicle, default 0)

  ref: https://github.com/google/or-tools/blob/b37d9c786b69128f3505f15beca09e89bf078a89/ortools/constraint_solver/routing.h#L907-L911
- [optional] A penalty cost for any dropping node using AddDisjunction() (default all nodes are mandatory)

  ref: https://github.com/google/or-tools/blob/b37d9c786b69128f3505f15beca09e89bf078a89/ortools/constraint_solver/routing.h#L606-L624 
- [optional] A linear penalty cost per node if using SoftCumulVar Lower/Upper Cost (to simulate earliness/tardiness) (default only hard limit [0, vehicle max capacity aka horizon of the dimension])

  ref: https://github.com/google/or-tools/blob/b37d9c786b69128f3505f15beca09e89bf078a89/ortools/constraint_solver/routing.h#L2514-L2523

  ref: https://github.com/google/or-tools/blob/b37d9c786b69128f3505f15beca09e89bf078a89/ortools/constraint_solver/routing.h#L2536-L2546

Misc/Not tested yet:

- [optional] Soft constraint a group of node to be visited by the same vehicle

  ref: https://github.com/google/or-tools/blob/b37d9c786b69128f3505f15beca09e89bf078a89/ortools/constraint_solver/routing.h#L675-L679

note: You can search for "soft" which means add extra cost to objective if not fulfilled while hard constraint must be respected... 

[Priidik Vilumaa]

Great list! Maybe this should be a pinned post or in the routing solver docs/guide to explain the objective function?

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[igor r]

Thank you.

And is there a formula how they are all combined together to get a final score?

[Laurent Perron]

the weighted sum of all of them with the coefficient given in the  API.

Laurent Perron | Operations Research | lpe...@google.com | (33) 1 42 68 53 00

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[amihai...@gmail.com]

Great post mizux - thx!
Is there a way to add a coefficient to the arc cost's sum? Or it should be done via the callback?

[Laurent Perron]

via the callback.

Laurent Perron | Operations Research | lpe...@google.com | (33) 1 42 68 53 00

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[igor r]

Thanks.

1. Can the coefficients be: a) negative  b) float ?

2. Is it possible to set the engine to look for max instead min? 

3. Can the cost be set to be negative?

[Laurent Perron]

all arc evaluators must be >= 0.

Demand evaluator can be negative, but the cumulvar are always >=0.

The solver does not support floats.

I do not know about cost weights. I would say > 0.

Laurent Perron | Operations Research | lpe...@google.com | (33) 1 42 68 53 00

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[igor r]

So, is there a proper way to find a maximum instead of a minimum?

How can I set the conditions to find the longest route?