[Cmpl] A couple of questions

[Mike Steglich]

Hi Michal,

Thank you for your interest in CMPL.

1) Tupel-sets
We think also that tupel-sets (multi-dimensional sets)  are a "must have" of a mathematical programming language. 
Therefore we are implementing tupel-sets and a new data file format at the moment.  
Please download a CMPL presentation (INFORMS 2011) that gives you an impression about these new CMPL features (beginning at slide 12).
http://www.coliop.org/download/cmplInforms2011.pdf

I think (hope) that we will release this  version in April/May.

Until the release of the new version you can use a workaround.  The idea is to have a matrix that contains the valid combinations of indices and to use this matrix for the definition of the variables, objective function and the constraints. 

For the transportation problem I have defined a matrix r for the valid routes between the sources i and the destinations j. 
r[,] := ( (1,1), (1,2) , (1,4), (2,2), (2,3) , (2,4), (3,1) , (3,3) );
The elements of r are used for the definition of the variables x[i,j].
x[ r[i,1],r[i,2] ] 
The entire problem can be formulated as follows:
parameters:
	plants  := 1(1)3;
	centers := 1(1)4;
	s[plants]  := (5000,6000,2500);
	d[centers] := (6000,4000,2000,1500);

	c[plants,centers] := ( (3,2,7,6), (7,5,2,3),(2,5,4,5) );
	#relevant routes
	r[,] := ( (1,1), (1,2) , (1,4), (2,2), (2,3) , (2,4), (3,1) , (3,3) );

variables:
	#definition of the vector x is based on the relevant routes in r[,]
	{ i in defset(r[,1]) : 	x[ r[i,1],r[i,2] ]: real[0..]; }

objectives:
	costs: sum{i in defset(r[,1]) : c[ r[i,1],r[i,2] ] * x[ r[i,1],r[i,2] ] } ->min;

constraints:
	#extended by a check whether a x[i,j] is a valid route
	supplies {i in plants  : sum{j in centers, count(x[i,j])>0 : x[i,j]  } <= s[i];}
	demands  {j in centers : sum{i in plants,  count(x[i,j])>0 : x[i,j]  } =  d[j];} 
 
This is actually not a smart approach but it works.

2) You are right, in CMPL all entities are declared and initiated at the same moment. 
I assume that you want to implement and test a model independently from the (real) data.  
Our idea is to create and test a model with dummy data. The values of the sets and parameters can be read by using include or readcsv() (and later with the CMPL new data file format). 
For solving a real problem you only have to exchange the dummy date file by your real data file.  

3) GPL / EPL
This issue is (unfortunately) still under discussion. As you mentioned we have got some requests in this mailing list that I answered directly and not via the mailing list. I had also a discussion with Kipp Martin (COIN-OS).

We like the idea of "give and take" and we think that GPL is the best way to share software in this manner.  But we see also the problem that GPL isn't compatible to EPL and to commercial licenses if the source code is to be shared. Therefore we are looking for approaches to avoid these problems. One alternative is to have a dual license (GPL or EPL). The second possibility is to grant an individual license to a specific project. 

But this issue is only relevant if you want to share source code.  If you only want to use CMPL as an external process (e.g. via Java ProcessBuilder) then you don' have any license problems.  


Cheers

Mike


Am 02.02.2012 um 09:58 schrieb Michal Kaut:

> Hello,
> 
> We are considering using CMPL (it looks very promising), but have a couple of
> questions first:
> 
> 1. Looking at the examples in the manual, I do not see any multi-dimensional
> sets. For example, in the Transportation problem, if we did not have all-to-all
> links, I would find it natural to define set 'links' being a subset of 'plants X
> centers' and index 'c' on that set. The objective would then be
>  costs: sum{(i, j) in links : c[i,j] * x[i,j] } ­->min;
> Is this possible in CMPL?
> And if not, can I at least define c only on a subset of 'plants X centers'
> (without giving the subset a name)?
> 
> 2. As far as I can see, all entities are declared and initiated at once - does
> it mean that it is not possible to declare an entity (for ex. to say that S is a
> set), and give it values some time later?
> 
> 3. I guess you do not like this question, since you did not respond to it
> previously, but I try nevertheless: why GPL? Would you at least consider dual
> licensing with CPL or EPL, to make it compatible with the other Coin-OR projects?
> 
> 
> Thanks a lot in advance.
> 
> Regards,
> Michal Kaut
> _______________________________________________
> Cmpl mailing list
> Cmpl at list.coin-or.org
> http://list.coin-or.org/mailman/listinfo/cmpl


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