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## Re: [Help-glpk] Subject to two conditions

 From: Michael Hennebry Subject: Re: [Help-glpk] Subject to two conditions Date: Wed, 10 Nov 2010 10:00:49 -0600 (CST) User-agent: Alpine 1.00 (DEB 882 2007-12-20)

```On Wed, 10 Nov 2010, Suleyman Demirel wrote:

```
```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.
```
```
Nyet.
M should be the smallest value which will work.
Merely large values give loose constraints.
Truly huge values can cause numerical difficulties.

```
```s.t. condition1{(i,j) in E}: (sum{(i,j,i1,j1) in L} x2[i1,j1] <=M *y;
```
```
Each of the above M's should at most be an upper
bound on the corresponding sum on the left.

```
```s.t. condition1{(i,j) in E}: (sum{(i,j,i1,j1) in L} x2[i1,j1] >=2*y - M
*(1-y)
```
```
Each of these M's should be at most an upper bound on
the negative of the corresponding sum on the left.

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