How to use it
- 1. Assign trucksClick a truck chip, then a door. Click an assigned chip to send it back.
- 2. Read the GanttBars start when the door is free and the truck has arrived; the gap after arrival is waiting.
- 3. CompareYour total wait vs the greedy earliest-free-door rule vs the exact optimum.
- 4. Change the dayEdit arrivals and unload times with the steppers, or roll a new day.
The dock
Inbound trucks (arrival · unload min)
Auto-schedule
Greedy takes trucks in arrival order and gives each the door that can start it soonest. The optimum is found by checking all 3⁶ = 729 assignments.
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Total wait (min)
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Makespan (min)
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Avg flow time
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Door idle (min)
Unassigned trucks
Solid bar = unloading; hollow leader = the truck waiting at the door after arriving. Numbers are truck IDs.
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Your total wait
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Greedy rule
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Exact optimum
Try these experiments
- Beat the greedy rule - it commits early trucks without seeing the whole morning; look for a long truck it placed badly.
- Roll days until you find one where greedy is exactly optimal - when arrivals are spread out, myopia costs nothing.
- Give one truck a 90-minute unload: where does the optimum park it, and what happens to every truck behind it if you move it?
About this tool
The concept
Cross-docks live or die on door scheduling: freight flows straight from inbound to outbound, so a waiting truck is inventory on wheels.
How it works
This is parallel-machine scheduling with release dates (P|rᵢ|Σw): NP-hard in general, but six trucks on three doors can be enumerated exactly.
Winning strategy
Keep long unloads out of the way of tight arrival clusters, and remember: minimising waiting is not the same as minimising makespan - check both tiles.
Background: Cross-docking · Machine scheduling