[Scip] XOR constraints

[Jörg Pfähler]

Hi Micha & Stefan

Thanks for the replies. I missunderstood what xor does for more than 2 
variables. I thought it would still mean "only zero or one variable is set to 
1" for more than 2 variables. So an xor-constraint is actually not what I need 
for my model.

Best Regards,
Jörg

> Hi Jörg,
> 
> moreover you can decide whether an odd or even number of (binary)
> variables needs to be set to true, to fulfill an XOR constraint. This is
> done by either setting the right hand side to one or zero.
> If you have only two variables SCIP will aggregate these two variables and
> delete your constraint, since it is redundant.
> 
> Best, Micha
> 
> > Hi Jörg,
> > 
> > an xor(x_1, ..., x_n) is usually not equivalent to x_1 + x_2 + ... + x_n
> > <= 1. This is only the case for n = 2. An xor is satisfied if an odd
> > number of the variables is set to true. I just check the code. even in
> > the special case of n = 2, SCIP does not upgrade the xor constraint into
> > an (linear) variable bound constraint (cons_varbound.c). That is
> > something we could thing about.
> > 
> > Best Stefan
> > 
> > On 10/17/11 22:16, Jörg Pfähler wrote:
> >> Hi,
> >> 
> >> does SCIP somehow take advantage of an xor-constraint (only one of the
> >> binary
> >> variables x_1, ..., x_k is 1) created with SCIPcreateConsXor instead
> >> of
> >> creating an equivalent constraint (x_1 + ... + x_k<= 1) with
> >> SCIPcreateConsLinear?
> >> 
> >> Best Regards,
> >> Jörg
> >> 
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