Restriction to sort an array in Minizinc

Question

I am trying to build a model with a parameter n = 5 which represent the length of an array. The model also have a decision variable that takes the range 0..9 and involves two constraints. The first of all is that the sum of the values of the array must be equal to the product of values of this array and the last one must be that the order of the values should be sorted increasing.

I attach the code:

int: n = 5;    % Array length
var 0..9: x;

array[1..n] of var 1..n: V;

% Constraints
constraint sum(V) = product(V);    
constraint increasing(array[1..n] of var 1..n: V);    % Sort problem

solve satisfy;
output[show(V)];

Zayenz · Accepted Answer · 2020-11-23 09:15:13Z

4

If you want to add the constraint that the array V is ordered, you can use the increasing constraint from the library

include "globals.mzn";
% ...
constraint increasing(V);

You must also include the file "globals.mzn" which includes the definition of increasing.

The complete model is thus:

include "globals.mzn";
int: n = 5;    % Array length
var 0..9: x;

array[1..n] of var 1..n: V;

% Constraints
constraint sum(V) = product(V);    
constraint increasing(V);

solve satisfy;
output[show(V)];

edited Nov 23, 2020 at 9:15

Zayenz

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answered Nov 22, 2020 at 21:39

hakank

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Zayenz · Accepted Answer · 2020-11-23 08:17:21Z

2

When possible, using an existing constraint as indicated in the accepted answer is great. If there is no available constraint, it can be good to also know how to specify your own predicate.

A complete model including your own specification of increasing could look like the following.

int: n = 5;    % Array length
var 0..9: x;

array[1..n] of var 1..n: V;

predicate increasing(array[1..n] of var 1..n: V) =
    forall(i in 1..n-1) (
        V[i] <= V[i+1]
    );

% Constraints
constraint sum(V) = product(V);    
constraint increasing(V);

solve satisfy;
output[show(V)];

answered Nov 23, 2020 at 8:17

Zayenz

1,97412 silver badges12 bronze badges

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