1. Announcements Appeals on Q8 based on correct calculation with bad input will be heard Appeals will not be successful on the basis of: –Running out of time –Copying the wrong cell –Order of weights on the WMA question For next class read Crazy Joey’s p. 77

2. MGTSC 352 Lecture 11: Aggregate Planning Case 2: Mountain Wear Set up and use solver to find minimum cost plan Air Alberta

3. Tradeoffs: “So which one of those did you want?” (pg. 50) ProductionInventoryWorkforceOvertime Plan 1LevelChangingLevel0 Plan 2Chase500Changing0 Plan 3Chase500LevelChanging Level and chase:

4. Mountain Wear … Can we find the lowest cost plan with solver?

5. Active Learning: Formulate Mountain Wear Problem in English 1 min., in pairs Template: –Maximize / minimizes … –By changing … –Subject to …

6. 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?

7. Air Alberta (pg. 72) Air Alberta is doing aggregate planning of flight attendant staffing for the next 6 months. They have forecast the number of flight attendant hours needed per month for March to August, based on scheduled flights, and wish to determine how many new attendants to hire each month. Each trained attendant on staff supplies 150 hours per month. A newly hired attendant is called a trainee during the first month, and each trainee’s net contribution is negative (-100 hours) because (s)he requires supervision, which detracts from the productivity of other attendants. Each trained attendant costs $1500 in salary and benefits per month while each trainee costs $700 per month. Normal attrition (resignations and dismissals) in this occupation is high, 10% per month, so Air Alberta never has any planned layoffs. Trainees are hired on the first day of each month and become attendants on the first day of the next month (with no attrition). As of March 1, Air Alberta has 60 trained attendants. Go to Excel

8. What do you mean hire 1.413 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

9. 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

10. Air Alberta (pg. 73) 1. Solver settings to find a least cost staffing plan: 2. The least cost staffing plan: 3. The total cost of this plan is $ 4. In which month does Air Alberta have the most excess attendant hours? 5. Air Alberta is considering running extra charter flights requiring 1000 flight attendant hours in either June or July. Which month would you choose to minimize total staffing costs? Why?

11. 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

12. What does it mean? gap = (5.1 – 3.8)/5.1 = 25% Solver stops when “gap” is less than “integer tolerance”

13. Changing the default Standard Solver Change to zero Premium Solver Options  Integer Options  Set “integer tolerance” to zero