Re: [Help-glpk] More conditional variables fun

[Yaron Kretchmer]

Thanks Michael
Yes, the differences (and the variables themselves) are bounded. We can denote the the upper/lower limit for each variable/difference by the constants l(x) and u(x). 

What would the formulation be in that case?

Regards
Yaron

On Mon, Oct 12, 2009 at 7:39 PM, Michael Hennebry <address@hidden> wrote:

This might bounce from the list.
NDSU is mucking with my return address.

Kretchmer wrote:

Thanks Larry. What I was looking for is for a way of forcing the "C"
variable to equal values per the truth table.

If "C" was binary I could achieve this by a series of inequalities without
big M, and I'm just wondering what would be the formulation for non-binary
variables.

In my previous post, I seem to have misinterpreted the question.

Unless you have bounds on the differences in the variables,
there isn't any good way.
With bounds on the differences,
the feasible sets of (a,b,c-d) and (a,b,c-e)
have four extreme points.
Their convex hulls are tetrahedra.

Now I'd like to be able to model conditional non-binary variables. Does
anybody know how to formulate this in mathprog?

----------Begin Description -------------------
*) a,b are binary
*) c,d,e is continuous.
*) I'd like c to be
   - 0 if a=b=0
   - d if a=0,b=1
   - e if a=1,b=0
   - 0 if a=b=1
----------End Description

--
Michael   address@hidden
"Pessimist: The glass is half empty.
Optimist:   The glass is half full.
Engineer:   The glass is twice as big as it needs to be."