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Nội dung chính- Which priority rule is used when jobs are processed according to the lowest ratio of due date to remaining processing time?What are the priority rules for job sequencing?Which rule establishes priorities on the basis of the due date for the jobs?What is the SPT priority rule?
- n jobs 1 machine case
- Priority rules Comparative measures
Scheduling -- determine the timing and order of operations to optimize the use of resources to meet production requirements
n jobs 1 machine case
Priority rules (pg.590)
First Come First Serve (FCFS)
Shortest Processing Time (SPT)
Earliest Due Date (EDD)
Slack Time Remaining (STR) = time remaining
before due date - remaining processing time
The shortest STR goes first
Critical Ratio (CR) = Time remaining before due date/Remaining processing time
The smallest CR goes first
Comparison of priority rules
Average Completion time/Mean flow time =(Total processing time + total waiting time)/Number of jobs
Average lateness = total late days/number of jobs
Example
Given:
Job
Processing time (days)
Due Date (days hence)
Slack time remaining
Critical Ratio
A 20 30 10 1.5 B 30 50 20 1.7 C 10 25 15 2.5 D 16 80 64 5.0 E 18 60 42 3.3FCFS
Proc. Time
Flow Time
Due Date
Lateness
A
20
20
30
0
B
30
50
50
0
C
10
60
25
35
D
16
76
80
0
E
18
94
60
34
Total
94
300
245
69
Mean
60
13.8
SPT
Proc.
Flow
Time to
Lateness
Seq.
Time
Time
Due
C
10
10
25
0
D
16
26
80
0
E
18
44
60
0
A
20
64
30
34
B
30
94
50
44
Total
94
238
245
78
Mean
47.6
15.6
SLACK
Proc.
Flow
Time to
Lateness
Seq.
Time
Time
Due
A
20
20
30
0
C
10
30
25
5
B
30
60
50
10
E
18
78
60
18
D
16
94
80
14
Total
94
282
245
47
Mean
56.4
9.4
CR
Proc.
Flow
Time to
Lateness
Seq.
Time
Time
Due
A
20
20
30
0
B
30
50
50
0
C
10
60
25
35
E
18
78
60
18
D
16
94
80
14
Total
94
302
245
67
Mean
60.4
13.4
EDD
Proc.
Flow
Time to
Lateness
Seq.
Time
Time
Due
C
10
10
25
0
A
20
30
30
0
B
30
60
50
10
E
18
78
60
18
D
16
94
80
14
Total
94
272
245
42
Mean
54.4
8.4
Comparing the priority rules
Rule
Mean Flow Time
Mean Lateness
FCFS
60
13.8
SPT
**47.6
15.6
STR
56.4
9.4
CR
60.4
13.4
EDD
54.4
**8.4
Exercises
Pg. 607 Problem 5, 13
Flow shop scheduling
n jobs two machines: all jobs require the same sequence/order in visiting the machines
Johnson's rule
If the shortest time is for the first machine, do the job first
If the shortest time is for the second machine, do the job last
Job
Processing Time, M1
Processing Time, M2
A
5
2
B
3
6
C
8
4
D
10
7
E
7
12
Job sequence: B à E à D à C à A
Gantt Chart representation
Exercises
Pg. 606 Problem 3, 9, 12, 14
Which priority rule is used when jobs are processed according to the lowest ratio of due date to remaining processing time?
SPT (shortest processing time). The job with the shortest processing time is processed first. This rule reduces work-in-process inventory, average job completion (flow) time, and average job lateness. EDD (earliest due date).What are the priority rules for job sequencing?
studies, the following four sequencing rules are included: (1) Shortest processing time rule (2) Slack per operation rule (3) First-in, first-out rule (4) Due date rule.Which rule establishes priorities on the basis of the due date for the jobs?
Earliest Due Date Sometimes called due date assignment, it places the highest priority on processing jobs with the earliest due dates.What is the SPT priority rule?
Under the SPT condition, short jobs on station three and independently competing short jobs on station two were given priority stations one and two. In the bottleneck priority condition, the longest jobs destined for station three took priority stations one and two over all other jobs. Tải thêm tài liệu liên quan đến nội dung bài viết What priority rule is being used when jobs are processed according to the lowest ratio of due date to remaining process time?