What is johnsons rule?

Johnson's rule is a production scheduling algorithm used to minimize makespan, which refers to the total time it takes to complete all jobs. The algorithm minimizes makespan by arranging the order in which jobs are processed across two or more machines.

The rule is named after RW Johnson, who developed it in 1954. It is particularly useful in situations where each job must follow a specific sequence of tasks performed on different machines.

Johnson's rule involves four steps:

1. Identify the jobs to be scheduled and the machines on which they will be processed.
2. For each job, identify the processing time required on each machine.
3. Determine the processing order for each job. This involves comparing the processing times on each machine for each job and selecting the optimal order that minimizes makespan.
4. Schedule the jobs according to the determined processing order.

Johnson's rule has been widely used in manufacturing, production planning, and operations management. It is often applied in situations where there are limited resources, tight schedules, and complex processing sequences.