Find solution using dual simplex method
MAX Z = -15x1 - 10x2
subject to
-3x1 - 5x2 <= -5
-5x1 - 2x2 <= -3
and x1,x2 >= 0; Solution:Note: This is dual simplex method, which is different from primal problem to dual problem conversion method
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Problem is | Max `Z` | `=` | ` - ` | `15` | `x_1` | ` - ` | `10` | `x_2` |
|
| subject to |
| ` - ` | `3` | `x_1` | ` - ` | `5` | `x_2` | ≤ | `-5` | | ` - ` | `5` | `x_1` | ` - ` | `2` | `x_2` | ≤ | `-3` |
|
| and `x_1,x_2 >= 0; ` |
The problem is converted to canonical form by adding slack, surplus and artificial variables as appropiate
1. As the constraint-1 is of type '`<=`' we should add slack variable `S_1`
2. As the constraint-2 is of type '`<=`' we should add slack variable `S_2`
After introducing slack variables| Max `Z` | `=` | ` - ` | `15` | `x_1` | ` - ` | `10` | `x_2` | ` + ` | `0` | `S_1` | ` + ` | `0` | `S_2` |
|
| subject to |
| ` - ` | `3` | `x_1` | ` - ` | `5` | `x_2` | ` + ` | `` | `S_1` | | | | = | `-5` | | ` - ` | `5` | `x_1` | ` - ` | `2` | `x_2` | | | | ` + ` | `` | `S_2` | = | `-3` |
|
| and `x_1,x_2,S_1,S_2 >= 0` |
| Tableau-1 | `C_j` | `-15` | `-10` | `0` | `0` | |
| `C_B` | `"Basis"` | `x_1` | `x_2` | `S_1` | `S_2` | `RHS` |
| `R_1` `0` | `S_1` | `-3` | `(-5)` | `1` | `0` | `-5``->` |
| `R_2` `0` | `S_2` | `-5` | `-2` | `0` | `1` | `-3` |
| | `Z_j` | `0` | `0` | `0` | `0` | `Z=0` |
| | `C_j-Z_j` | `-15` | `-10` | `0` | `0` | |
| | `"Ratio"=(C_j-Z_j)/(S_1,j)` and `S_1,j<0` | `(-15)/(-3)` `=5` | `(-10)/(-5)` `=2``uarr` | `(0)/(1)` `=`--- | `(0)/(0)` `=`--- | |
Most negative `RHS` is `-5` and its row index is `1`. So,
the leaving basis variable is `S_1`.
Least positive ratio is `2` and its column index is `2`. So,
the entering variable is `x_2`.
`:.`
The pivot element is `-5`.
Entering `=x_2`, Departing `=S_1`, Key Element `=-5`
`R_1`(new)`= R_1`(old) `-: -5`
| `x_1` | `x_2` | `S_1` | `S_2` | `RHS` |
| `R_1`(old) = | `-3` | `-5` | `1` | `0` | `-5` |
| `R_1`(new)`= R_1`(old) `-: -5` | `0.6` | `1` | `-0.2` | `0` | `1` |
`R_2`(new)`= R_2`(old) + `2 R_1`(new)
| `x_1` | `x_2` | `S_1` | `S_2` | `RHS` |
| `R_2`(old) = | `-5` | `-2` | `0` | `1` | `-3` |
| `R_1`(new) = | `0.6` | `1` | `-0.2` | `0` | `1` |
| `2 xx R_1`(new) = | `1.2` | `2` | `-0.4` | `0` | `2` |
| `R_2`(new)`= R_2`(old) + `2 R_1`(new) | `-3.8` | `0` | `-0.4` | `1` | `-1` |
| Tableau-2 | `C_j` | `-15` | `-10` | `0` | `0` | |
| `C_B` | `"Basis"` | `x_1` | `x_2` | `S_1` | `S_2` | `RHS` |
| `R_1` `-10` | `x_2` | `0.6` | `1` | `-0.2` | `0` | `1` |
| `R_2` `0` | `S_2` | `(-3.8)` | `0` | `-0.4` | `1` | `-1``->` |
| | `Z_j` | `-6` | `-10` | `2` | `0` | `Z=-10` |
| | `C_j-Z_j` | `-9` | `0` | `-2` | `0` | |
| | `"Ratio"=(C_j-Z_j)/(S_2,j)` and `S_2,j<0` | `(-9)/(-3.8)` `=2.3684``uarr` | `(0)/(0)` `=`--- | `(-2)/(-0.4)` `=5` | `(0)/(1)` `=`--- | |
Most negative `RHS` is `-1` and its row index is `2`. So,
the leaving basis variable is `S_2`.
Least positive ratio is `2.3684` and its column index is `1`. So,
the entering variable is `x_1`.
`:.`
The pivot element is `-3.8`.
Entering `=x_1`, Departing `=S_2`, Key Element `=-3.8`
`R_2`(new)`= R_2`(old) `-: -3.8`
| `x_1` | `x_2` | `S_1` | `S_2` | `RHS` |
| `R_2`(old) = | `-3.8` | `0` | `-0.4` | `1` | `-1` |
| `R_2`(new)`= R_2`(old) `-: -3.8` | `1` | `0` | `0.1053` | `-0.2632` | `0.2632` |
`R_1`(new)`= R_1`(old) - `0.6 R_2`(new)
| `x_1` | `x_2` | `S_1` | `S_2` | `RHS` |
| `R_1`(old) = | `0.6` | `1` | `-0.2` | `0` | `1` |
| `R_2`(new) = | `1` | `0` | `0.1053` | `-0.2632` | `0.2632` |
| `0.6 xx R_2`(new) = | `0.6` | `0` | `0.0632` | `-0.1579` | `0.1579` |
| `R_1`(new)`= R_1`(old) - `0.6 R_2`(new) | `0` | `1` | `-0.2632` | `0.1579` | `0.8421` |
| Tableau-3 | `C_j` | `-15` | `-10` | `0` | `0` | |
| `C_B` | `"Basis"` | `x_1` | `x_2` | `S_1` | `S_2` | `RHS` |
| `R_1` `-10` | `x_2` | `0` | `1` | `-0.2632` | `0.1579` | `0.8421` |
| `R_2` `-15` | `x_1` | `1` | `0` | `0.1053` | `-0.2632` | `0.2632` |
| | `Z_j` | `-15` | `-10` | `1.0526` | `2.3684` | `Z=-12.3684` |
| | `C_j-Z_j` | `0` | `0` | `-1.0526` | `-2.3684` | |
| | Ratio | | | | | |
Since all `C_j-Z_j <= 0` and all `RHS >= 0`, thus the current solution is the optimal solution.
Hence, optimal solution is arrived with value of variables as :
`x_1=0.2632,x_2=0.8421`
Max `Z=-12.3684`
This material is intended as a summary. Use your textbook for detail explanation.
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