What is restricted assignment problem?

In free or unrestricted assignment problem all jobs can be performed by all

individuals or all machines. But, in practice, it is possible that a particular worker is
not competent perform a particular job. In such situation that job can not be
assigned to that corresponding worker. This is known as restricted assignment
problem. To handle this problem of restriction on job assignment correspond cell ‘—
——‘ (dash) is consider and no algebraic steps are perform at this cell. In optimal
solution that combination of assignment is not possible.