Module6 Flashcards
Main Models (Module 6)
- Capacitated plant location model (with single sourcing)
- Gravity location model
- Minimum spanning-tree problems
- Traveling salesman problem
Facility Location Info
- Location of supply sources and markets
- Demand and/or forecast
- Cost factors (facility, labor, production, material)
- Inventory costs (region/site & function of quantity)
- Transportation costs between regions/sites
- Taxes and tariffs
Types of CPL Models
not very relevant / insightful in my opinion
- Capacitated plant location models (Region)
- Capacitated plant location models (Site)
CPL Model Structure
- Decision: Open/close plants, how much to produce/ship
- Fixed costs: If plant is open
- Capacities: Max production per plant
- Demands: Regions need certain amounts
- Variable costs: For transporting each unit
CPL Model Parameters
Capacitated Plant Location
- fi: Fixed cost to open Plant i
- cij: Cost/unit from Plant i to Region j
- Ki: Capacity of Plant i
- Dj: Demand of Region j
CPL Decision Variables
- yi ∈ {0,1}: 1 if Plant i is open, 0 otherwise
- xij ≥ 0: Quantity shipped from Plant i to Region j
CPL Model Formulation
Objective: Minimize
∑(fi·yi) + ∑∑(cij·xij)
Constraints:
- Demand: ∑ xij = Dj for each j
- Capacity: ∑ Dj·xij ≤ Ki·yi
- Binary open/closed: yi = 0 or 1
- Nonnegative shipments: xij ≥ 0
Capacitated Plat Location
CPL with Single Sourcing
- Similar to CPL, but each demand region is served by exactly one plant.
- xij becomes binary: region j assigned to plant i or not.
Gravity Model Concept
- Places customers as points on a plane (xn, yn)
- Finds a center of gravity (x, y) that minimizes total distance cost
- Continuous optimization in 2D
Gravity Model Objective
Minimize: ∑ (distancen · Dn · Fn)
- distancen = (Euclidean from (x,y) to (xn, yn))
- Dn = quantity
- Fn = shipping cost/unit/mile
Gravity Model Solution
- Non-linear objective (square root in distance)
- Solved via iterative or quadratic programming methods
- No closed-form formula for the final (x, y)
Minimum Spanning Tree
- Goal: Connect all nodes with minimal total link cost
- Applies to telecommunication, roads, pipelines, etc.
- Ensures no cycles and all nodes are reachable
MST Algorithm
Minimum Spanning Tree
- Start with cheapest link.
- Repeatedly add the next cheapest link that connects a new node.
- Stop when all nodes are connected.
Traveling Salesman Problem
- Must visit each city exactly once and return to start.
- Objective: Minimize total travel cost/distance.
- Known to be NP-complete (non-deterministic polynomial time).
Nearest Neighbor Heuristic (TSP)
- Pick a start node.
- Move to closest unvisited node.
- Repeat until all are visited, then return to start.
TSP Complexity
Travelling Salesman Problem
- Number of routes grows factorially with number of cities
- No efficient (polynomial-time) exact algorithm is known
- Heuristics needed for large problems
TSP & NP-completeness
- TSP is a representative NP-complete problem
- Clay Mathematics Institute offers $1M prize for a general solution
- Illustrates computational complexity in supply chain optimization
SunOil Case Example
- Global petrochemical plants in 5 regions
- Considering low (10M units) or high (20M units) capacity plants
- Trade-off: Economies of scale vs. transportation costs
Natural Beverages Example
to be deleted in my opinion
- Considering a new bottling facility in Hamburg or Bremen
- Possibly building one new warehouse in same city
- Capital limit: €1 million
Steel Appliances Example
- One current factory in Denver
- Need a second factory in eastern US
- Minimizes transportation to/from supply sources & markets
- Used a Gravity Model approach
Heuristic Methods
- Provide good feasible solutions fast
- Not guaranteed optimal
- Often greedy or iterative
Capacity & Demand Constraints
- Supply constraints ensure feasible capacity usage
- Demand constraints ensure all demands are met
Inventory Costs
- Vary by location and quantity
- Key factor in total supply chain cost
Transportation Costs
- Depend on distance and volume shipped
- Influence whether to centralize or decentralize facilities