Analysis of Performance of Different Job-sequencing Rules:
There may be severer criteria for evaluating the job sequencing rules. Some of them are given as follows :
- Average number of jobs in the system.
- Average lateness of the job.
- Mean tardiness of the job.
- Cost of changeover.
- Average flow time.
For evaluating the performance of the job-sequencing rules. A comparative study among some of the priority rules has been done. For that, a single machine is considered where, 4 jobs ought to be processed. The following data is given to evaluate the performance.
Table: Data Description
Case I : SPT Rule
The following flow time has been found with the SPT based job sequencing rule:
Table: Flow Time of SPT Based Sequencing
From the above analysis, total flow time may be easily calculated. Total flow time
= 175 + 395 + 640 + 990 = 2200 min.
Though, average flow time = 2200/4 = 550 min.
Now, compare the due date of the job with it flow time. From the comparison it has been discovered that Job (J3) and Job (J1) shall be on time, whereas, Job (J4) and Job (J2) will be late by some amount of time.
Therefore, average lateness of the jobs = (0 + 0 + 20 + 210)/4 = 60 min.