Solver phase
After creating the initial solution or already starting with it, the solver run every phase that has been specified in the solver options.
A phase behaves almost like the whole solving process. It starts with the highest temperature and cools down as the iterations increase.
There are four phases that can be used.
- Distance cost only phase
- Restarts phase
- Full costs phase
- Full costs with noise
| Phase | What it does | Why? |
| Distance cost only phase | All vehicles have all costs set to zero except for the distance cost, which is set to 1. | Used when complicated distance costs are in place to first make the solver try to use as little distance and possible (usually prefering the large vehicles to do the far away jobs and more of them).
Then after that is done, revert to the normal costs and the solver will find efficiency with them. Example: There are two types of vehicles in place. A - 0,6 $ / km. Capacity 10 B - 1 $ / km. Capacity 20. There are number or jobs with 1-2 demands all over the map. The solver would start giving the far away jobs to the cheap vehicles and having bit of a hard time later swapping them (especially if the total capacity of the fleet is close to the total amount delivered). Human planner would try to place as many as possible gouped far away calls on the big trucks. When you set the distance cost to 1 it will prefer to use big capacities and far away jobs (in the initial solution creation as well) |
| Restarts phase | Restarts the solving specified number of times. After allocated iterations are used selects the found solution from all the restarts. | To reduce the variance at the cost of some time. Sometimes the solution quality depends a lot on the first couple initial iterations, which can lead the solver to one or another solution regions.
Restarting helps to select the "best" starting region. |
| Full costs phase | Standart costs apply.
Default. |
Most iterations should happen here. |
| Full costs with noise | Standart costs apply, during the insertion cost calculation a small value is added to the cost and thus the solver can choose slightly different insertion. | If things are bit too stale in the end of solving. |
Add Solver phase
1) Open Solver options
2) Add % of iterations to different phases.
How do they work with the phases?
Simply put the total number of iterations is split in between all the planned phases.
Example:
- You set the total number of iterations to 25 000.
- You set the number of restart phases to 5
- You set the Restart phases % to 10.
- You set the Only distance cost iterations % to 20.
There will be:
2500 iterations in the Restart phase
- 500 in each of the 5 restart phases ( 100 spent on Only distance cost iterations, 400 on the Full costs)
4500 iterations in the Distance cost only phase.
18000 iterations in the Full cost phase