mknapsack | R Documentation |

Solves the 0-1 (binary) multiple knapsack problem.

mknapsack(w, p, cap)

`w` |
vector of (positive) weights. |

`p` |
vector of (positive) profits. |

`cap` |
vector of capacities of different knapsacks. |

Solves the 0-1 multiple knapsack problem for a set of profits and weights.

A multiple 0-1 knapsack problem can be formulated as:

```
maximize vstar = p(1)*(x(1,1) + ... + x(m,1)) + ...
... + p(n)*(x(1,n) + ... + x(m,n))
subject to
w(1)*x(i,1) + ... + w(n)*x(i,n) <= cap(i) for i=1,...,m
x(1,j) + ... + x(m,j) <= 1 for j=1,...,n
x(i,j) = 0 or 1 for i=1,...,m , j=1,...,n ,
```

The multiple knapsack problem is reformulated as a linear program and
solved with the help of package `lpSolve`

.

This function can be used for the single knapsack problem as well,
but the 'dynamic programming' version in the `knapsack`

function
is faster (but: allows only integer values).

The solution found is most often not unique and may not be the most compact
one. In the future, we will attempt to 'compactify' through backtracking.
The number of backtracks will be returned in list element `bs`

.

A list with components, `ksack`

the knapsack numbers the items are
assigned to, `value`

the total value/profit of the solution found, and
`bs`

the number of backtracks used.

Contrary to earlier versions, the sequence of profits and weights has been interchanged: first the weights, then profits.

The compiled version was transferred to the `knapsack`

package on
R-Forge (see project 'optimist').

Kellerer, H., U. Pferschy, and D. Pisinger (2004). Knapsack Problems. Springer-Verlag, Berlin Heidelberg.

Martello, S., and P. Toth (1990). Knapsack Problems: Algorithms and Computer Implementations. John Wiley & Sons, Ltd.

Other packages implementing knapsack routines.

## Example 1: single knapsack w <- c( 2, 20, 20, 30, 40, 30, 60, 10) p <- c(15, 100, 90, 60, 40, 15, 10, 1) cap <- 102 (is <- mknapsack(w, p, cap)) which(is$ksack == 1) # [1] 1 2 3 4 6 , capacity 102 and total profit 280 ## Example 2: multiple knapsack w <- c( 40, 60, 30, 40, 20, 5) p <- c(110, 150, 70, 80, 30, 5) cap <- c(85, 65) is <- mknapsack(w, p, cap) # kps 1: 1,4; kps 2: 2,6; value: 345 ## Example 3: multiple knapsack p <- c(78, 35, 89, 36, 94, 75, 74, 79, 80, 16) w <- c(18, 9, 23, 20, 59, 61, 70, 75, 76, 30) cap <- c(103, 156) is <- mknapsack(w, p, cap) # kps 1: 3,4,5; kps 2: 1,6,9; value: 452 ## Not run: # How to Cut Your Planks with R # R-bloggers, Rasmus Baath, 2016-06-12 # # This is application of multiple knapsacks to cutting planks into pieces. planks_we_have <- c(120, 137, 220, 420, 480) planks_we_want <- c(19, 19, 19, 19, 79, 79, 79, 103, 103, 103, 135, 135, 135, 135, 160) s <- mknapsack(planks_we_want, planks_we_want + 1, planks_we_have) s$ksack ## [1] 5 5 5 5 3 5 5 4 1 5 4 5 3 2 4 # Solution w/o backtracking # bin 1 : 103 | Rest: 17 # bin 2 : 135 | Rest: 2 # bin 3 : 79 + 135 | Rest: 6 # bin 4 : 103 + 135 + 160 | Rest: 22 # bin 5 : 4*19 + 2*79 + 103 + 135 | Rest: 8 # # Solution with reversing the bins (bigger ones first) # bin 1 : 103 | Rest: 4 # bin 2 : 2*19 + 79 | Rest: 20 # bin 3 : 79 + 135 | Rest: 6 # bin 4 : 2*19 + 79 + 135 + 160 | Rest: 8 # bin 5 : 2*103 + 2*135 | Rest: 17 # # Solution with backtracking (compactification) # sol = c(1, 4, 4, 1, 1, 3, 4, 5, 5, 5, 5, 4, 2, 3, 4) # bin 1 : 2*19 + 79 | Rest: 3 # bin 2 : 135 | Rest: 2 # bin 3 : 79 + 135 | Rest: 6 # bin 4 : 2*19 + 79 + 135 + 160 | Rest: 8 # bin 5 : 3*103 + 135 | Rest: 36 ## End(Not run)

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