1. Find dual from primal conversion
MAX z = x1 - x2 + 3x3
subject to
x1 + x2 + x3 <= 10
2x1 - x2 - x3 <= 2
2x1 - 2x2 - 3x3 <= 6
and x1,x2,x3 >= 0
Solution:
Primal is (Solution steps of Primal by Simplex method)
MAX `z_x` | `=` | `` | `` | `x_1` | ` - ` | `` | `x_2` | ` + ` | `3` | `x_3` |
|
subject to |
`` | `` | `x_1` | ` + ` | `` | `x_2` | ` + ` | `` | `x_3` | ≤ | `10` | `` | `2` | `x_1` | ` - ` | `` | `x_2` | ` - ` | `` | `x_3` | ≤ | `2` | `` | `2` | `x_1` | ` - ` | `2` | `x_2` | ` - ` | `3` | `x_3` | ≤ | `6` |
|
and `x_1,x_2,x_3 >= 0; ` |
In primal, There are `3` variables and `3` constraints, so in dual there must be `3` constraints and `3` variables
In primal, The coefficient of objective function `c_1=1,c_2=-1,c_3=3` becomes right hand side constants in dual
In primal, The right hand side constants `b_1=10,b_2=2,b_3=6` becomes coefficient of objective function in dual
In primal, objective function is maximizing, so in dual objective function must be minimizing
Let `y1,y2,y3` be the dual variables
Dual is (Solution steps of Dual by Simplex method)
MIN `z_y` | `=` | `` | `10` | `y_1` | ` + ` | `2` | `y_2` | ` + ` | `6` | `y_3` |
|
subject to |
`` | `` | `y_1` | ` + ` | `2` | `y_2` | ` + ` | `2` | `y_3` | ≥ | `1` | `` | `` | `y_1` | ` - ` | `` | `y_2` | ` - ` | `2` | `y_3` | ≥ | `-1` | `` | `` | `y_1` | ` - ` | `` | `y_2` | ` - ` | `3` | `y_3` | ≥ | `3` |
|
and `y_1,y_2,y_3 >= 0; ` |
This material is intended as a summary. Use your textbook for detail explanation.
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