[SCIP] Can't use "max" in a constraint where "sum" works

[Marc Pfetsch]

This means that what you want cannot currently be expressed using ZIMPL. 
The reason is that this is not a linear expression anymore (in contrast 
to sums).

If your x-variables have upper bounds M, you could reformulate this by 
using additional variables something like this:

var z;
var y[S] binary;
subto M1: forall <s> in S: z >= x[s];
subto M2: forall <s> in S: z <= x[s] + M * (1 - y[s]);
subto C: sum <s> in S: y[s] == 1;
...

I am not saying that this is the best way in your case - the example 
should rather show that you need to work a bit in order be applicable.



On 17/03/2025 15:57, Göran Uddeborg wrote:
> Hello!
> 
> I'm doing my first attempts in using scip (version 9.1.1 on Fedora
> 41). Some simple test cases for learning the tool went fine, but when
> I got to my real problem, I don't seem to be able to get the zimpl
> syntax correct. If I use the "sum" function, scip accepts the code,
> but if I use "max" in the same place it doesn't. I don't find any
> explanation in the documentation or FAQs.
> 
> To illustrate the problem, I've cut down my example to this:
> 
>      set S := { 1..3 };
>      var x[S];
>      subto c:
>        sum <f> in S : x[f] >= 10;
>      minimize m:
>        sum <f> in S : x[f];
> 
> That above code works, I do get a solution. However if I replace one
> of the "sum" with "max" it doesn't work any more.
> 
>      set S := { 1..3 };
>      var x[S];
>      subto c:
>        max <f> in S : x[f] >= 10;
>      minimize m:
>        sum <f> in S : x[f];
> 
> That gives a syntax error.
> 
> What am I doing wrong? What is it I miss?
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