sci.op-research

Dnia Fri, 21 Mar 2008 13:40:32 -0700 (PDT)
"xgeneral57@gmail.com" napisa=C5=82(a):

> On Mar 21, 4:30=C2=A0pm, Wit Jakuczun wrote:
> > Dnia Fri, 21 Mar 2008 13:13:32 -0700 (PDT)
> > "xgenera...@gmail.com" napisa=C5=82(a):
> >
> > > I have a set of continuous variables x(i), i=3D1,.., N where x(i) can=
be
> > > negative, zero or positive. I'm trying to count, in some way, how many
> > > of x(i)'s are exactly zero. Is there any way to do so using linear
> > > constraints?
> >
> > Without introducing binary variables it is not possible. This means
> > you must switch to MIP. Moreover x(i)'s must be bounded.
> >
> > Best regards
> > --
> > [ Wit Jakuczun =C2=A0 =C2=A0 ]
> > [ WLOG Solutions =C2=A0http://www.wlogsolutions.com]
>=20
> x(i)'s ae actually bounded above and below: LB(i) <=3D x(i) <=3D UB(i).
> But the problem is that x(i)'s can be either positive or negative.

Represent each x(i) with a sum of two auxiliary variables that
cannot be greater than zero at the same time.

Best
--=20
[ Wit Jakuczun ]
[ WLOG Solutions http://www.wlogsolutions.com ]