Please enable JavaScript.
Coggle requires JavaScript to display documents.
operations scheduling - Coggle Diagram
operations scheduling
specific sequencing rules
measures of system performance
FCFS
First-come, first-served
Jobs are processed in the sequence in which they entered the shop
SPT
Shortest processing time
increasing order of their processing time
shortest processing time is first
Minimize
mean flow time
mean waiting time
mean lateness for singel-machine squencing
EDD
Earliesr due date
increasing order of their due dates
the earliest due date is first
Minimize
the number of tardy jobs
the maximum tardiness with precedence constraints
no matter how late it is (not depend on the amount of lateness)
Step1
Sequence-the earliest due date to obtain the initial solution
Step2
Find the first tardy job i (none exits to step4)
Step3
Reject the job with the largest processing time(return to step2) in jobs(1-i)
Step4
Form an optimal sequence by taking the current sequence and appending to it the rejected jobs
The jobs appended to the current sequence maybe scheduled in any order becasue the consititute the tardy jobs
CR
Critical ratio
smallest critical ratio
(Due Date - Current Time) / Processing Time
smaller
as the current time approaches the due date (the jobs with the longer processing times)
negative
the job is late, automatically scheduled next
more than one late job , then the late jobs are scheduled in SPT sequence
Evaluate
The Mean Flow Time
Flow Time
the waiting time + the job processing time
The flow time of job i = the completion time of job i
Average Tardiness
Tardiness
the job is completed prior to its due date
equal to zero
the job is completed after its due date
equal to the number of days
Tardiness = Completed Time - Due Date
the positive part of lateness
lateness
earliness is the negative part of lateness
Lateness = Fow time for job i - Due date for job i
Number of Tardy Jobs
Precedence Constraints
Lawler's Algorithm
single machine scheduling