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I was playing around with the new KnapsackSolve function in Mathematica 11 and came across something odd that I don't understand. Perhaps someone could shed some light on this for me. Here's my dataset:

data = <|"two" -> {1, 2, 1}, "three" -> {1, 3, 1}, "four" -> {1, 4, 1}|>

When I call KnapsackSolve for various target values:

KnapsackSolve[data,2]
<|"two" -> 1, "three" -> 0, "four" -> 0|>
KnapsackSolve[data,3]
<|"two" -> 1, "three" -> 0, "four" -> 0|>
KnapsackSolve[data,4]
<|"two" -> 0, "three" -> 1, "four" -> 0|>
KnapsackSolve[data,5]
<|"two" -> 1, "three" -> 1, "four" -> 0|>

I was expecting 2 to give "two" - correct but 3 and 4 give unexpected answers, then 5 gives me "two" and "three".

I've set the costs to be all maxcounts all be to 1 and payoffs to be 1 also. What am I doing wrong?

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You are trying to maximize c1+c2+c3 subject to 2c1+3c2+4c2<=n, where all variables are either 0 or 1.

For n=2 there is only one answer, c1=1,c2=0,c3=0.

For n=3 there are two answers, c1=1,c2=0,c3=0 as given, or c1=0,c2=1,c3=0.

For n=4 there are three answers, c1=0,c2=1,c3=0 as given, or c1=1,c2=0,c3=0, or c1=0,c2=0,c3=1.

For n=5 there is only one answer c1=1,c2=1,c3=0.

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  • $\begingroup$ I understand, so I'm only getting the first answer back that fulfils the criteria rather than the complete set of answers then. It's not clear from the documentation that all results are not returned - but then again all of the examples only return a single set! $\endgroup$ – FractalDoctor Nov 30 '16 at 20:20

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