Edson

Many solvers behave as you describe. These solvers get local information about the function, compute a step and repeat. Baron is a global solver. To do its work it needs full info on the functional form and algebra used to describe the problem. It accepts a limited number of functions in this problem description. Log is ok but log2 not. Other global solvers behave similarly but each has it’s own list of allowed functions.

Steve

Sent from my iPhone

On Sep 27, 2012, at 3:03 AM, Edson Cordeiro do Valle wrote:

```
Hello
That's strange, I thought that GAMS evaluated the function, gradient and hessian values, and send them to external solvers based on the external solver requests. After the receiving these information from GAMS, the solver (in this case, Baron), calculates a new step and/or search direction and "ask" for equations evaluation to GAMS again.
```

Can anyone explains how the information flows with GAMS and external sovers works?

Regards.

2012/9/26 Steven Dirkse

```
Richard,
BARON does not have a log2() function, but it has a log. If you use a
macro you can easily convert log2 to the natural logarithm. Just add
this line to the start of your model. BARON handles it OK then.
$macro log2(x) (log(x)/log(2))
-Steve
On Tue, Sep 25, 2012 at 5:10 AM, Richard O. Afolabi
wrote:
> We are trying to run BARON with this simple code but everytime it reports
> "Cannot handle function 'log2' " This code below is a sample code which is
> different from our original problem.
>
>> variables x, y, z;
>> x.lo = 1; x.up = 4;
>> y.lo = 4; y.up = 4;
>> equations o;
>> o.. z =e= power(x,3) - sqr(2*y) + log2(x) + log2(10*y+2);
>> Option MINLP = BARON;
>> model m / o /;
>> solve m using minlp min z;
>> Display x.l, y.l;
>
>
> I'm hoping that someone might know a work around for solving a MINLP problem
> involving Log2(x) function.
>
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--
Steven Dirkse, Ph.D.
GAMS Development Corp., Washington DC
Voice: (202)342-0180 Fax: (202)342-0181
<sdirkse@gams.com>
http://www.gams.com
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```

–

Edson Valle

edsoncv@gmail.com

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