On Fri, 2015-05-01 at 15:17 +0000, Agostina Kodelia wrote: > Hi! > I'm solving a very simple postman travelling problem with > the glp_intopt method. When I retrieved the column value > with glp_mip_col_val, it returns a negative zero. The zero is alright, > but I don't understand why has a minus, could anyone explain to me why > is this happening? >
This is because the IEEE 754 standard which most of modern FPUs conform to claims that a floating-point zero has the sign bit. A negative zero may appear, for example, on computing (2. - 3.) * (5. - 5.) = -1. * +0. = -0. For details see http://en.wikipedia.org/wiki/IEEE_754-1985#Zero . > > Thanks in advance!! > > > Agostina. > > > PS: This is the problem. > > > Minimize > Z: + 10 Y01 + 20 Y12 + 30 Y20 + 60 Y21 + 70 Y02 + 80 Y10 > > > Subject To > C1: + Y20 + Y10 = 1 > C2: + Y21 + Y01 = 1 > C3: + Y12 + Y02 = 1 > C4: + Y12 + Y10 = 1 > C5: + Y02 + Y01 = 1 > C6: + Y21 + Y20 = 1 > > > Bounds > 0 <= Y01 <= 1 > 0 <= Y12 <= 1 > 0 <= Y20 <= 1 > 0 <= Y21 <= 1 > 0 <= Y02 <= 1 > 0 <= Y10 <= 1 > > > End > > > _______________________________________________ Help-glpk mailing list [email protected] https://lists.gnu.org/mailman/listinfo/help-glpk
