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Unformatted text preview: and there may be multiple operations on some
Parallel processing vs. sequential processing: parallel
processing means that the machines are identical.
Flow time of job i: Time elapsed from initiation of first job
until completion of job i.
Makespan: Flow time of the job completed last.
Tardiness: The positive difference between the
completion time and the due date.
Lateness: Difference between completion time and due
date (may be negative). Common Sequencing Rules
FCFS. First Come First Served. Jobs processed
in the order they come to the shop.
SPT. Shortest Processing Time. Jobs with the
shortest processing time are scheduled first.
EDD. Earliest Due Date. Jobs are sequenced
according to their due dates.
CR. Critical Ratio. Compute the ratio of
processing time of the job and remaining time
until the due date. Schedule the job with the
largest CR value next.
largest 5 Example
Job Number Processing Time
2 Due Time
Apply the following rules:
First come, first served
Shortest processing time (minimize mean flow time)
Earliest due date (minimize maximum lateness)
Critical Ratio Scheduling
Critical 6 Sequencing for Single Machine
Minimize mean flow time (SPT)
Minimize maximum lateness (EDD)
Minimize the number of tardy jobs (Moore’s
Precedence constraints (Lawler’s algorithm)
Precedence Multiple Machine Sequencing
Assume that several jobs must be processed on
more than one machine. (e.g. n jjobs...
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This document was uploaded on 03/23/2014.
- Spring '14