为什么我的数组是 var int 类型而不是 var set of int？

Question

I have the following problem: I want to call the global constraint at_most but I got an error related to the signature

constraint forall(i in 0..w-1)(at_most(l_max, [board[i,j] | j in 0..l_max-1], 0..n));

the second argument does not match because it turns out to be var int instead of var set of int but I have previously defined board in this way:

set of int: VALUES = 0..n;
array[0..w-1,0..l_max-1] of var VALUES: board;

Answer 1

Just as a general message: at_most is among the list of deprecated constraints: https://www.minizinc.org/doc-2.5.5/en/lib-globals.html#deprecated-constraints . Instead, you should use a count constraint. These constraints are more flexible and better supported by the solvers.

In this case there seems to be a misconception about what at_most does. At most only restrict the number of time a single value occurs. You are. however, giving it a full set of values.

If you are counting all the different values, then you instead can useglobal_cardinality_low_up . (You might also want to look at the closed version). I think you meant to write the following constraint.

constraint forall(i in 0..w-1)(
  global_cardinality_low_up([board[i,j] | j in 0..l_max-1], 0..n, [0 | i in 0..n], [l_max | i in 0..n])
);

This constraint insure that for the comprehensions the values in 0..n only occur l_max times.

Note that if you are using the comprehension to select a full row, then it would be better to use slice notation: board[i,..] .