On Nov 18, 10:15 am, jason <

[hidden email]> wrote:

> Can anyone help me with this?

>

> In a constratint, i want to describe "K is not equal to L" in ampl

> mod file. But, how?

I assume K and L are variables? Introduce a binary variable Y. If K

and L are both integer variables (so that the minimum absolute

difference would be 1), you can add the constraints

K >= L + 1 - m*Y

L >= K + 1 - m*(1-Y)

where m is an upper bound on |K-L|+1.

If K and L are divisible variables, I think you'll have to introduce a

parameter d > 0 which is the minimum difference you will tolerate.

(You cannot require |K-L| > 0; that would make the feasible region

open. What you can require is |K-L| >= d > 0.) Again, add the binary

variable Y and compute an upper bound m on |K-L| + d, and repeat the

constraints above replacing 1 with d.

/Paul

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