[Scip] Changing the bounds of a FIXED variable

[Vivek Periaraj]

Hi Gerald,

Thanks.

1) Make sense. That's why I was unable to change them. I do this for pricing but I think that's a wrong approach.I was trying the approach suggested in http://scip.zib.de/doc-2.0.2/html/FAQ.html. I guess that's for earlier version and no longer applicable.
2) I want to delete variables before solving. The reason is I want to get the mapping of the variables in the RMP to be in sync with the variables in the original problem. So I first create the variables, get the variable pointers for each index for the variables of the original problem. At this point, I would like to delete those variables that are not part of the initial RMP. This way I could ensure the computations of the reduced costs and pricing of new variables to be mapped to the original problem. If I do SCIPdelVar(), it's marked for deletion but the variable data is still present in the problem. Can I achieve the same thing as what CPXdelsetcols() does in CPLEX?

Regards,
Vivek.

----- Original Message ----- 

From: "Gerald Gamrath" <gamrath at zib.de> 
To: "Vivek Periaraj" <vivek.periaraj at gmail.com> 
Cc: scip at zib.de 
Sent: Monday, March 11, 2013 9:29:51 PM 
Subject: Re: [Scip] Changing the bounds of a FIXED variable 

Dear Vivek, 

1) If a variable is fixed to some value, both bounds get changed to that 
value. Why do you want to change the bounds afterwards? Do you want to 
relax them? That is not possible during the solving process (because it 
would mean that all the dual bound computed so far, nodes cut off, etc. 
might be wrong because they were based on the fixing). 
2) During solving, you also cannot just delete variables, because of 
similar reasons and some more (the variable might be part of a solution, 
SCIP might have branched on it,...). However, you can mark them to be 
deleted automatically during pricing and if they aged out of the LP at 
the node where they were created, they will automatically be deleted, if 
possible. Please have a look at the FAQ where this is described in more 
detail: http://scip.zib.de/doc/html/FAQ.shtml#Q5.11 

Best, 
Gerald 

On 11.03.2013 16:47, Vivek Periaraj wrote: 
> Hello, 
> 
> 1) Is there a way to change the bounds of a fixed variable? I fix it using SCIPfixVar() but SCIPchgVarLb() and SCIPchgVarUb() does not allow me to change the bounds. 
> 2) How to delete a variable from the problem object. If I do SCIPdelVar(), the variable is marked for deletion but it's not deleted from the problem object. 
> 
> Regards, 
> Vivek 
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