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Operations Management

Operations Management. Module C – Transportation Models. PowerPoint presentation to accompany Heizer/Render Principles of Operations Management, 7e Operations Management, 9e. Outline. Transportation Modeling Developing an Initial Solution The Northwest-Corner Rule

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Operations Management

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  1. Operations Management Module C – Transportation Models PowerPoint presentation to accompany Heizer/Render Principles of Operations Management, 7e Operations Management, 9e

  2. Outline • Transportation Modeling • Developing an Initial Solution • The Northwest-Corner Rule • The Intuitive Lowest-Cost Method • The Stepping-Stone Method • Special Issues in Modeling • Demand Not Equal to Supply • Degeneracy

  3. Learning Objectives When you complete this module you should be able to: Develop an initial solution to a transportation models with the northwest-corner and intuitive lowest-cost methods Solve a problem with the stepping-stone method Balance a transportation problem Solve a problem with degeneracy

  4. Transportation Modeling • An interactive procedure that finds the least costly means of moving products from a series of sources to a series of destinations • Can be used to help resolve distribution and location decisions

  5. Transportation Modeling • A special class of linear programming • Need to know • The origin points and the capacity or supply per period at each • The destination points and the demand per period at each • The cost of shipping one unit from each origin to each destination

  6. Transportation Problem Table C.1

  7. Boston (200 units required) Cleveland (200 units required) Des Moines (100 units capacity) Albuquerque (300 units required) Evansville (300 units capacity) Fort Lauderdale (300 units capacity) Transportation Problem Figure C.1

  8. Des Moines capacity constraint Factory capacity To Albuquerque Boston Cleveland From $5 $4 $3 100 Des Moines Cell representing a possible source-to-destination shipping assignment (Evansville to Cleveland) $8 $4 $3 300 Evansville $9 $7 $5 300 Fort Lauderdale Warehouse requirement 300 200 200 700 Cost of shipping 1 unit from Fort Lauderdale factory to Boston warehouse Clevelandwarehouse demand Total demand and total supply Transportation Matrix Figure C.2

  9. Northwest-Corner Rule • Start in the upper left-hand cell (or northwest corner) of the table and allocate units to shipping routes as follows: • Exhaust the supply (factory capacity) of each row before moving down to the next row • Exhaust the (warehouse) requirements of each column before moving to the next column • Check to ensure that all supplies and demands are met

  10. Northwest-Corner Rule Assign 100 tubs from Des Moines to Albuquerque (exhausting Des Moines’s supply) Assign 200 tubs from Evansville to Albuquerque (exhausting Albuquerque’s demand) Assign 100 tubs from Evansville to Boston (exhausting Evansville’s supply) Assign 100 tubs from Fort Lauderdale to Boston (exhausting Boston’s demand) Assign 200 tubs from Fort Lauderdale to Cleveland (exhausting Cleveland’s demand and Fort Lauderdale’s supply)

  11. To (A) Albuquerque (B) Boston (C) Cleveland Factory capacity From $5 $4 $3 100 100 (D) Des Moines $8 $4 $3 200 100 300 (E) Evansville $9 $7 $5 100 200 300 (F) Fort Lauderdale Warehouse requirement 300 200 200 700 Means that the firm is shipping 100 bathtubs from Fort Lauderdale to Boston Northwest-Corner Rule Figure C.3

  12. Route From To Tubs Shipped Cost per Unit Total Cost D A 100 $5 $ 500 E A 200 8 1,600 E B 100 4 400 F B 100 7 700 F C 200 5 $1,000 Total: $4,200 Northwest-Corner Rule Computed Shipping Cost This is a feasible solution but not necessarily the lowest cost alternative Table C.2

  13. Intuitive Lowest-Cost Method Identify the cell with the lowest cost Allocate as many units as possible to that cell without exceeding supply or demand; then cross out the row or column (or both) that is exhausted by this assignment Find the cell with the lowest cost from the remaining cells Repeat steps 2 and 3 until all units have been allocated

  14. To (A) Albuquerque (B) Boston (C) Cleveland Factory capacity From $5 $4 $3 100 100 (D) Des Moines $8 $4 $3 300 (E) Evansville $9 $7 $5 300 (F) Fort Lauderdale Warehouse requirement 300 200 200 700 Intuitive Lowest-Cost Method First, $3 is the lowest cost cell so ship 100 units from Des Moines to Cleveland and cross off the first row as Des Moines is satisfied Figure C.4

  15. To (A) Albuquerque (B) Boston (C) Cleveland Factory capacity From $5 $4 $3 100 100 (D) Des Moines $8 $4 $3 100 300 (E) Evansville $9 $7 $5 300 (F) Fort Lauderdale Warehouse requirement 300 200 200 700 Intuitive Lowest-Cost Method Second, $3 is again the lowest cost cell so ship 100 units from Evansville to Cleveland and cross off column C as Cleveland is satisfied Figure C.4

  16. To (A) Albuquerque (B) Boston (C) Cleveland Factory capacity From $5 $4 $3 100 100 (D) Des Moines $8 $4 $3 200 100 300 (E) Evansville $9 $7 $5 300 (F) Fort Lauderdale Warehouse requirement 300 200 200 700 Intuitive Lowest-Cost Method Third, $4 is the lowest cost cell so ship 200 units from Evansville to Boston and cross off column B and row E as Evansville and Boston are satisfied Figure C.4

  17. To (A) Albuquerque (B) Boston (C) Cleveland Factory capacity From $5 $4 $3 100 100 (D) Des Moines $8 $4 $3 200 100 300 (E) Evansville $9 $7 $5 300 300 (F) Fort Lauderdale Warehouse requirement 300 200 200 700 Intuitive Lowest-Cost Method Finally, ship 300 units from Albuquerque to Fort Lauderdale as this is the only remaining cell to complete the allocations Figure C.4

  18. To (A) Albuquerque (B) Boston (C) Cleveland Factory capacity From $5 $4 $3 100 100 (D) Des Moines $8 $4 $3 200 100 300 (E) Evansville $9 $7 $5 300 300 (F) Fort Lauderdale Warehouse requirement 300 200 200 700 Intuitive Lowest-Cost Method Total Cost = $3(100) + $3(100) + $4(200) + $9(300) = $4,100 Figure C.4

  19. To (A) Albuquerque (B) Boston (C) Cleveland Factory capacity From $5 $4 $3 100 100 (D) Des Moines $8 $4 $3 200 100 300 (E) Evansville $9 $7 $5 300 300 (F) Fort Lauderdale Warehouse requirement 300 200 200 700 Intuitive Lowest-Cost Method This is a feasible solution, and an improvement over the previous solution, but not necessarily the lowest cost alternative Total Cost = $3(100) + $3(100) + $4(200) + $9(300) = $4,100 Figure C.4

  20. Stepping-Stone Method Select any unused square to evaluate Beginning at this square, trace a closed path back to the original square via squares that are currently being used Beginning with a plus (+) sign at the unused corner, place alternate minus and plus signs at each corner of the path just traced

  21. Stepping-Stone Method Calculate an improvement index by first adding the unit-cost figures found in each square containing a plus sign and subtracting the unit costs in each square containing a minus sign Repeat steps 1 though 4 until you have calculated an improvement index for all unused squares. If all indices are ≥ 0, you have reached an optimal solution.

  22. (A) Albuquerque (B) Boston (C) Cleveland To Factory capacity From $5 $4 $3 100 100 (D) Des Moines - $8 $4 $3 200 100 300 (E) Evansville - + $9 $7 $5 100 200 300 (F) Fort Lauderdale Warehouse requirement 300 200 200 700 100 1 99 $8 $4 $5 $4 + - - + 201 99 200 100 Stepping-Stone Method Des Moines- Boston index = $4 - $5 + $8 - $4 = +$3 + Figure C.5

  23. To (A) Albuquerque (B) Boston (C) Cleveland Factory capacity From $5 $4 $3 Start 100 100 (D) Des Moines - $8 $4 $3 200 100 300 (E) Evansville + - $9 $7 $5 100 200 300 (F) Fort Lauderdale + - Warehouse requirement 300 200 200 700 Stepping-Stone Method + Des Moines-Cleveland index = $3 - $5 + $8 - $4 + $7 - $5 = +$4 Figure C.6

  24. To (A) Albuquerque (B) Boston (C) Cleveland Factory capacity From $5 $4 $3 100 100 (D) Des Moines $8 $4 $3 200 100 300 (E) Evansville $9 $7 $5 100 200 300 (F) Fort Lauderdale Warehouse requirement 300 200 200 700 Stepping-Stone Method Evansville-Cleveland index = $3 - $4 + $7 - $5 = +$1 (Closed path = EC - EB + FB - FC) Fort Lauderdale-Albuquerque index = $9 - $7 + $4 - $8 = -$1 (Closed path = FA - FB + EB - EA)

  25. Stepping-Stone Method If an improvement is possible, choose the route (unused square) with the largest negative improvement index On the closed path for that route, select the smallest number found in the squares containing minus signs Add this number to all squares on the closed path with plus signs and subtract it from all squares with a minus sign

  26. To (A) Albuquerque (B) Boston (C) Cleveland Factory capacity From $5 $4 $3 100 100 (D) Des Moines $8 $4 $3 + 200 100 300 (E) Evansville - $9 $7 $5 100 200 300 (F) Fort Lauderdale - Warehouse requirement 300 200 200 700 Stepping-Stone Method + Add 100 units on route FA Subtract 100 from routes FB Add 100 to route EB Subtract 100 from route EA Figure C.7

  27. To (A) Albuquerque (B) Boston (C) Cleveland Factory capacity From 100 $5 $4 $3 100 (D) Des Moines 100 200 $8 $4 $3 300 (E) Evansville 100 200 $9 $7 $5 300 (F) Fort Lauderdale Warehouse requirement 300 200 200 700 Stepping-Stone Method Total Cost = $5(100) + $8(100) + $4(200) + $9(100) + $5(200) = $4,000 Figure C.8

  28. Special Issues in Modeling • Demand not equal to supply • Called an unbalanced problem • Common situation in the real world • Resolved by introducing dummy sources or dummy destinations as necessary with cost coefficients of zero

  29. Factory capacity To (A) Albuquerque (B) Boston (C) Cleveland Dummy From $5 $4 $3 0 250 250 (D) Des Moines $8 $4 $3 0 300 50 50 200 (E) Evansville $9 $7 $5 0 300 150 150 (F) Fort Lauderdale Warehouse requirement 850 300 200 200 150 Special Issues in Modeling Total Cost = 250($5) + 50($8) + 200($4) + 50($3) + 150($5) + 150(0) = $3,350 New Des Moines capacity Figure C.9

  30. Special Issues in Modeling • Degeneracy • To use the stepping-stone methodology, the number of occupied squares in any solution must be equal to the number of rows in the table plus the number of columns minus 1 • If a solution does not satisfy this rule it is called degenerate

  31. To Customer 1 Customer 2 Customer 3 Warehouse supply From $8 $2 $6 100 100 Warehouse 1 $10 $9 $9 0 100 120 20 Warehouse 2 $7 $10 $7 80 80 Warehouse 3 Customer demand 100 100 100 300 Special Issues in Modeling Initial solution is degenerate Place a zero quantity in an unused square and proceed computing improvement indices Figure C.10

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