Re: [Help-glpk] [Fwd: Get the MIp relative gap at the end of the optimization]

[oguyon]

Thank you Andrew and Xypron,

So, I've implemented a callback function for my purpose. Here is my code :

public void callback(glp_tree tree) {
        long now = System.currentTimeMillis();
        if(now - start >= 5000){
                double mipGap = GLPK.glp_ios_mip_gap(tree);
                if(mipGap <= 0.01){
                        GLPK.glp_ios_terminate(tree);
                }
        }               
}

But I still have a problem. The function GLPK.glp_ios_terminate(tree) does
not make exactly what I want. In fact, it terminates the search by setting a
status GLPKConstants.GLP_UNDEF to my model (even if GLPK has found an
integer feasible solution). it's a problem for me. 

Does anyone know how to make a better termination of my program through the
callback function, in order to get a status GLPKConstants.GLP_FEAS if an
integer solution has already been found.

Thank you,
Olivier


xypron wrote:
> 
> Hello Olivier,
> 
>> > I'm using glpk 4.45 through a Java environnement (JRE 1.6.0_24).
>> 
>> I don't know details how the callback is implemented in the Java
>> interface. In C its entry point address is passed to glp_intopt thru the
>> glp_iocp control parameter block (2nd parameter).
> 
> GLPK for Java is available for download at
> http://glpk-java.sourceforge.net
> It comes with the following examples showing how to use callbacks:
> examples\java\Gmpl.java
> examples\java\GmplSwing.java
> 
> Documentation is provided in
> doc\glpk-java.pdf
> 
> In GLPK for Java method GLPK.glp_init_iocp(iocp) presets
> the address for the callback such that the C callback calls
> Java method GlpkCallback.callback(long cPtr).
> 
> You need an object of a class implementing interface 
> org.gnu.glpk.GlpkCallbackListener.
> 
> You register it with
> GlpkCallback.addListener(listener);
> 
> When a callback occurs method callback of the listener is called.
> 
> To find out the reason why the callback is called use
> int reason = GLPK.glp_ios_reason(tree);
> 
> You may compare it to constants like
> GLPKConstants.GLP_IBINGO
> 
> To stop listening use
> GlpkCallback.removeListener(listener);
> 
> Best regards
> 
> Xypron
> 
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