The Assignment problem can be of Minimization type or Maximization type.
A Minimization Assignment problem involves cost, time or distance data. The objective of solution is to minimize the final answer.
A Maximization Assignment problem involves sales, revenue or profit data. The objective of solution is maximization of the final answer. We need to first convert the Maximization problem in Minimization problem. This conversion is called Regret matrix. From the original profit values, we find out the highest profit value. From this highest profit, we subtract all profit values. The resulting matrix is Regret matrix.