Mountain Wear - Introduction to Operations Management - Lecture Slides, Slides of Production and Operations Management

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Aggregate Planning

Case 2: Mountain Wear

Set up and use solver to find minimum cost plan

Air Alberta

Tradeoffs: “So which one of those

did you want?” (^) (pg. 50)

Production Inventory Workforce Overtime

Plan 1 Level Changing Level 0

Plan 2 Chase 500 Changing 0

Plan 3 Chase 500 Level Changing

Level and chase:

Active Learning : Formulate

Mountain Wear Problem in English

• 1 min., in pairs
• Template:
  • Maximize / minimizes …
  • By changing …
  • Subject to …

Extending the

Mountain Wear Formulation

• How do we fire 10.625 people
• Should we include additional constraints?
  • Limit on overtime?
  • Limit on hirings / firings? -?
• How do the additional constraints impact

cost?

What do you mean hire 1.

attendants?

• You can’t do that, right?
  • Right.
  • But: sometimes it’s better to ignore such

details

• Especially if the numbers are large:
  • Not much difference between hiring 123 and 124

people, so might as well allow fractional values

Integer Constraints:

Include or leave out?

For

• More realistic

Against

• No sensitivity report
• May take longer to

solve

• Not that important if

numbers are big

More about Integer Constraints

• Problems with integer constraints

– Are harder for solver

– Can take a long time to find optimal solution

for large problems

– By default, solver stops when “within 5% of

optimal”

• What does it mean?

• How can we change the default?

Pg. 74

What does it mean?

x

y

Solution to LP relaxation, profit = 5.

Best known feasible solution (incumbent solution), profit = 3.

gap = (5.1 – 3.8)/5.

= 25%

Solver stops

when “gap” is less than “integer

tolerance”