1) IMPORTANT NOTE!!!!! Flashcards
When doing the constraints charts, the OFC has a coeffecicients at the top- do you drag them down to all the cells below??
NO!!!! only put coefficients in ur constraints if they come from something else sweetie
when doing lp graphing, how to note the constraints?
hash lines baby!! in the correct direction for every consrtaint besidse non negativity
IN LP graph corner point method! dont forget to what??
note the otpimal solution on the graph and also in the box!!!
HIGHLIGHT THE FEASIBLE REGION
YES
LABEL ALL CONSTRAINTS
PURR
how do you do integer constraint
ISO PROFIT LINE SHOULD BE A DASHED LINE
!!
IMPORTANT NOTE about the table in corner point method
not given to you in exam! so remember the format is
Co-ordinates Profit
in excel solver sensitivty, if there is an allowable increase/decrease to infintity.. what does this mean
you can increase or decrease up to an infinite amount and it will not impact the model!
if there is a complex ratio constraint:
<35% of total investment should be in xyz, what do I reference in my RHS constraint?
Reference the variable cells!!!!!
x y z <= 0.35*(uvwxyz)
excel solver, what does every cell in the constraints table need to be linked to?
(on the LHS of the constraint)
a decision variable that is going to change
how to calculate profit
((unit profit- unit cost)*quantity)
NOT SALES-COST
How to formulate the ofc
The line of the top with the variables and their coeffs (#2 A1)
JUST subtract price-cost for each individual element shawty!! And then put it in (don’t try to mathematically reason too hard it is illogical)
IMPORTANT REMINDER ABOTUT those a1 q2 table questions: what are the two things you write?
1) Maximize or minimize in the top left corner by the ofc!!
2) subject to: in the corner!
how to clean up a sensitivitty report?
2 decimals and 1e30+
how do you say if the solution is feasible
because all constraints satisfied
how do you say if solutions are not feasible
because all constraints are unsatisfied
how do you do the write ups in excel for allowable and non allowable decrease (compare the terms?)
ex: 1 is not in the allowable decrease of 0.75
(1>0.75)
how do you write up the write ups for the “All or none constraints”
NEVER re-solve w excel and say new profit
-just compare the money you earn from the all or none deal and the costs associated w all or none deal
($181.50 revenue > $150 costs)
do you write binding/non-binding for ip problems or lp problems
only ip problems
what colour cells do you multiply for the ofc
sumproduct (blue, yellow)
should you put in the int and bin constraint no matter what?
ALWAYS!!! NO MATTER WHAT!!! EVEN IF USELESS IN THE ASSIGNMENT AND TRANSPORT PROBLEMS
How to formulate ratio constraints?
1) Write out the constraint in words
2) Move your denominator to the RHS
-> this will be (decimal)*(sum(xx:xx)
3) The numerator is what you will be referencing for the constraints!
->Make sure that these cells meet BOTH the restrictions of the TOP AND BOTTOM
FOR SMA and WMA do you use actual or forecasted
use actual
when you square negative errors is it positive or negative
NEGATIVE
for exponential smoothing do you use forecasted or actual
actualalpha + 1-alphaforecasted
if error is positive:
if error is negative:
underestimation
overestimation
at-ft (at>ft) actual was more than forecasted; so we predicted less
at-ft(At<ft) actual was less than forecasted; so we predicted too high
how to calcualte base?
THIS IS JUST THE AVERAGE DEMAND PER SEASON
(total for all terms/number of terms)
total of year/12
How to calculate k
that is the number of this period!!!
-> if yearly, then k is between 1-12
-> if seasonally, then k is 1-4
how to calculate trend?
trend percent% x base
How to forecast for year 3?
1) Calculate the average monthly demand for year 2 (total for year 2/12) [this is the same as base]
2) then calculate the average for all the months (year 2+ year 1 / 2)
3) Calculate the cyclical index (average for the month / average monthly demand for year) basically divide the avg for the month by what is the average demand should be
4) Then calculate the forecast for year 3, take the (year 3 yearly demand/12) * (cyclical index)
How to forecast for year 3?
1) Calculate the average monthly demand for year 2 (total for year 2/12)
2) then calculate the average for all the months (year 2+ year 1 / 2)
3) Calculate the cyclical index (average for the month / average monthly demand for year) basically divide the avg for the month by what is the average demand should be
4) Then calculate the forecast for year 3, take the (year 3 yearly demand/12) * (cyclical index)
HOW TO calculate cyclical index
average for this month/ average monthly demand for all the months in the year
if they give u a constraint in cents how do you write it?
as it was given!! dont convert!
how to formulate the OFC for the constraint tables?
price-COST!!!
AND if not given price then just put the cost
when you choose the right forecasting technique, there is a tradeoff between
accuracy and cost
what is causual forecasting
forecasting related factors, promotional campagins, economic conditions, and compeititors actions
if you increase/decrease the ofc within the allowable decrease
the decision variables stay the same! problem does not need to be re-solved
if there is an allowable decrease, and you are measuring impact on profit, use what ?/
NEGATIVE SIGN!! IN THE DECREASE
Impact on profit= (-)change in resources*(shadow price)
what happens in transportation problem if both constraints are <=
you will get an answer of 0
what happens in transportation problem if both constraints are =
you will not get a solution
5 special conditions in LP problems
1) redundant constraints
2)alternate optimal solution
3) infeasible solution
4) non linearity
5) unbounded
how can you get more than one optimal solution
more than one optimal point found by solver
what are redundant constraints
non binding constraints
why do we keep redundant constraints
because we dont know if they are binidng prior to solving/ they could be binding in the future
when could you get an unbounded solution (ERROR)?
in investment problem with no highest amount of investment possible
how could you get non linearity error
IF you accidentally have decision variables being divided
How could you get infeasibility error
signs are wrong, feasible region is incorrect
