Solution
This is the cost matrix.
| 14 | 64 | 18 | 70 |
| 56 | 61 | 40 | 96 |
| 88 | 50 | 44 | 32 |
| 36 | 7 | 66 | 83 |
Subtract row minima
For each row, the minimum element is subtracted from all elements in that row.
| 0 | 50 | 4 | 56 | (-14) |
| 16 | 21 | 0 | 56 | (-40) |
| 56 | 18 | 12 | 0 | (-32) |
| 29 | 0 | 59 | 76 | (-7) |
Subtract column minima
Because each column already contains a zero, subtracting the column minima has no effect.
Cover all zeros with a minimum number of lines
A total of 4 lines are required to cover all zeros.
| 0 | 50 | 4 | 56 | x |
| 16 | 21 | 0 | 56 | x |
| 56 | 18 | 12 | 0 | x |
| 29 | 0 | 59 | 76 | x |
The optimal assignment
Because there are 4 lines required, an optimal assignment exists among the zeros.
| 0 | 50 | 4 | 56 |
| 16 | 21 | 0 | 56 |
| 56 | 18 | 12 | 0 |
| 29 | 0 | 59 | 76 |
This corresponds to the following optimal assignment in the original cost matrix.
| 14 | 64 | 18 | 70 |
| 56 | 61 | 40 | 96 |
| 88 | 50 | 44 | 32 |
| 36 | 7 | 66 | 83 |
The total minimum cost is 93.