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JOB SHOP SCHEDULIND PROBLEM > Coding: permutational with repetition

                                                                                                                                                                                                                                                               

 

Last update: 06/2011

 

 

  CODING

 

 The string size is mxn, where m is the number of machines (operations) and n is the number of jobs. Each string item is a random integer number between [1, n]. This number is repeated as many times as operations are required the job.

 

For instance, the string size for a 3 machines x 4 jobs problem is 12 (=3 x4). The job1 is represented by number 1 and it is repeated 3 times because the job 1 has 3 operations ( 3 machines). The process is the same for the other jobs. Thus, one possible result is: [ 1 2 4 4 3 2 3 4 1 1 ].

  

    DECODING
 

 

We decode the symbolic representation from left to right:

 

  • The first string's item is 1. It is the first 1. Thus it is decoded as job 1's first operation.

  • The second string's item is 2. It is the first 2. Thus it is decoded as job 2's first operation.

  • The third string's item is 4. It is the first 4. Thus it is decoded as job 4's first operation.

  • The forth string's item is 4. It is the second 4. Thus it is decoded as job 4's second operation.

  • The fifth string's item is 3. It is the first 3. Thus it is decoded as job 3's first operation.

  • The sixth string's item is 2. It is the second 2. Thus it is decoded as job 2's second operation.

  • The seventh string's item is 3. It is the second 3. Thus it is decoded as job 3's second operation.

  • The eighth string's item is 2. It is the third 2. Thus it is decoded as job 2's third operation.

  • The ninth string's item is 4. It is the third 4. Thus it is decoded as job 4's third operation.

  • The tenth string's item is 1. It is the second 1. Thus it is decoded as job 1's second operation.

  • The eleventh string's item is 1. It is the third 1. Thus it is decoded as job 1's third operation.

  • The twelfth string's item is 3. It is the third 3. Thus it is decoded as job 3's third operation.

 

     References

 

Mattfeld, D.C. (1995). Evolutionary search and the job shop. Investigations on genetic algorithms for production scheduling. Springer. Berlin

 

 

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