You have an either/or constraint, and I do not think you can use a direct or
statement (unless developers made something like that).
Usually, if you have an either/or constraint, you should define a binary
variable, say y, taking only 0-1 value. If y=0, the sum is less than zero,
if y=1, the sum is greater than two.
Let M be a very large number (M=100000000000).Then, you should have two
constraints as follows.
s.t. condition1{(i,j) in E}: (sum{(i,j,i1,j1) in L} x2[i1,j1] <=M *y;
s.t. condition1{(i,j) in E}: (sum{(i,j,i1,j1) in L} x2[i1,j1] >=2*y - M
*(1-y)
Hope this helps.
On Wed, Nov 10, 2010 at 9:18 AM, João Vilela <[email protected]>wrote:
> Dear all,
>
> I'm solving a variation of a max flow problem in a graph, where:
>
> set V, default {1..n}; /* is a set of nodes */
> set E, within V cross V; /* is a set of arcs */
> set L, within E cross E; /* is a set to map edges to edges */
> var x2{(i,j) in E}, binary; /* x2[i,j] indicates whether there is any
> flow going through link (i,j) */
>
> And I have the following condition:
>
> > s.t. condition{(i,j) in E}: (sum{(i,j,i1,j1) in L} x2[i1,j1] <=0) or
> (sum{(i,j,i1,j1) in L} x2[i1,j1] >= 2);
>
> Basically, this means that I need the sum of those x2[i1,j1] to be
> different from 1 (i.e. less or equal to 0 *or* bigger or equal than 2).
> Although, this code gives me the following error:
>
> "operand preceding <= has invalid type"
>
> Any idea?
>
> Thank you,
> Joao
>
> _______________________________________________
> Help-glpk mailing list
> [email protected]
> http://lists.gnu.org/mailman/listinfo/help-glpk
>
--
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Suleyman Demirel - Office: (734) 647-3167
PhD Candidate in Operations Management
Stephen M. Ross School of Business
University of Michigan, Ann Arbor
Web: http://www.umich.edu/~sdemirel
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