Scheduling and sequencing Flashcards
What is scheduling
Assignment of start and completion times to particular
jobs, people or equipment.
What is staff scheduling used for
To allocate labor to time based on forecasts and capacity, also concerns the full and part time mix
What are appointments
The reservation of staff and capacity to minimize idle time
What is sequencing
Calculation the optimal order of tasks, is verry complex and can only be done by hand for simple problems. Harder problems are simulated
Name a couple of process focused performance criteria mesures
Flow time (time of good in facility) and make span (time to process good)
How do you calculate flow time of a good
start time of job + its processing time
How do you calculate the make span of a group of goods
completion time of last good - start time of first good. How long it took to make the group of goods
Name some due date criteria measures
Lateness and tardyness
How do you calculate lateness
Completion time - due data
What is tardiness
The amount of time the completion time exeeds the due date
What are the pros and cons of FCFS first come first serve sequencing rule
It is fair but it disregards urgency and time it completes the order
Explain the Fewest number of operations remaining (FNO) sequencing rule
It prioritizes jobs proportionately closer to completion but ignores the actual length of the jobs
Explain the pros and cons of the Shortest processing time (SPT) sequening rule
It prioritizes the fastest jobs and tends to maximize resource utilizaation but if there are verry long problems they are at risk of tardiness
Explain the Earliest due date (EDD) sequencing rule
It prioritizes the jobs with the earlyest due date so it strives not to be tardy but does not tend to performe well on flow time, inventory time and so on
Wxplain the Least work remaining (LWR)
Prioritize the jobs that are done soonest, might de prioritize longer problems if new ones are added
Explain Jhonsons algortithm
An algorithm to find a minimum make span schedule for a facility with two processors doing different tasks so each job requeires some time in each machine.
Step 1 - List the jobs and their processing times on Resources #1 and #2
– Step 2 - Find the job with the shortest sequencing time
– Step 3 - If this time corresponds to Resource #1, sequence the job first; if it corresponds to resource #2, sequence the job last
– Step 4 - Repeat steps 2 and 3 using the next-shortest processing time. Work inward from both ends of the sequence until all jobs have been scheduled
What chart is most often sued to monitor sheduloing
Gantt aka bar charts
What is the Clarke–Wright Heuristic method for route sheduling
An algorithm which seeks to combine customers into longer routes to reduce the total time traveled
Step 1 - Compute the savings s(i,j) for all pairs of customers i and j
Step 2 - Find the pair of customers with the largest savings, and
determine if there is sufficient capacity to link those customers
together. New route is constructed if customers with the largest savings can be linked; if not, the next largest savings are tried.
Step 3 - Step 2 is applied as long as the next largest savings is
positive. Procedure is stopped when all positive savings have been considered
The arival of users into a system is generally a random event that follows the poisson process
True
What lambda makes the poisson distribution normal
Around 12
What probability distribution is most commonly used to describe service time
The exponential distribution
Explain the three part code describing various queuing systems
It is in the for of A/B/k where A identifies the arival distribution, B identifies the service or departure distribution and k the number of channels in the system.
Common distributions include M = Poisson/exponential, D = constant/ deterministic and G which has a known mean and variance
What are the little’s flow equations
The relationship between the time a unit spends in a queuing system and the number of units in a system
average number of units in system (L) = average arrival rate (l) * average time in the system(W)
What is the difference between FCFS and LCFS systems
First come last served vs last come first served, they should be the same
Name some characteristics of a M/M/1 queuing system
- Single channel
- Poisson arrival-rate distribution
- Exponential service-time distribution
- Unlimited maximum queue length
- Infinite calling population
- Examples:
– Single-window theatre ticket sales booth
– Single-scanner airport security station
How do you calculate the probability that a number of events will occur in a poisson distribution if you have the average
(A^N *e^-A)/N!
Average = A Number = N
How do you calculate the probability of getting more than a number in a poisson distribution
1 - Probability of getting all the numbers below the number you seek
What is the probability of getting a value below or equal to a number in an exponential distribution if you have the mean
1 - e^(-(1/mean)*value)
What is the probability of getting a value above a number in an exponential distribution if you have the mean
e^(-(1/mean)*value)
