<div dir="ltr">Hi Ambros,<div><br></div><div>Thanks a bunch for that trick, I appreciate it. That does work for me also. Learning more of these hidden gems day by day in ZIMPL and SCIP...</div><div><br></div><div>- George</div>
</div><div class="gmail_extra"><br><br><div class="gmail_quote">On Mon, Sep 23, 2013 at 1:19 AM, Ambros Gleixner <span dir="ltr"><<a href="mailto:gleixner@zib.de" target="_blank">gleixner@zib.de</a>></span> wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">Of course it should read c == 1 - vabs( a - b ).<br>
<br>
Am 23.09.2013 07:13, schrieb Ambros Gleixner:<div class="HOEnZb"><div class="h5"><br>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
Hi George,<br>
<br>
mathematically, you want c = 1 - |a-b|, and James' answer is the<br>
standard linearization for this. You can let Zimpl do this<br>
reformulation for you automatically by writing<br>
<br>
c == vabs( a - b )<br>
<br>
or using vabs( a - b ) directly in your constraints.<br>
<br>
Happy zimpling,<br>
<br>
Ambros<br>
<br>
<br>
<br>
<br>
Am 20.09.2013 03:25, schrieb George Nychis:<br>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
Haha, I had thought of that solution James. It seemed a little overkill<br>
to me, but maybe it is the only good way to do this. Let's see if<br>
someone can turn up with something better, and if all fails I'll settle<br>
for it. Thanks for pointing it out!<br>
<br>
<br>
On Thu, Sep 19, 2013 at 9:21 PM, James Gunning <James.Gunning@csiro.au<br>
<mailto:<a href="mailto:James.Gunning@csiro.au" target="_blank">James.Gunning@csiro.au</a><u></u>>> wrote:<br>
<br>
George, this may be completely dopey, but if one added a slack z to<br>
the objective, and equations<br>
z<=1, z>=a-b, z>= b-a, z=1-c (or some suitable simplification),<br>
that might work..<br>
<br>
George Nychis wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
This might be slightly off-topic, but I don't know where better to<br>
ask. I'm having a hard time expressing something in ZIMPL<br>
linearly. I have two variables a and b. I want the variable c to<br>
be strictly binary and take on the value of 1 when a and b are<br>
equal, and 0 otherwise. Does anyone know of a good way to express<br>
this?<br>
<br>
Thanks!<br>
George<br>
<br>
<br>
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