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|ID||Category||Severity||Reproducibility||Date Submitted||Last Update|
|0000329||[ALGLIB] Spec.functions||major||always||2010-05-07 22:52||2010-05-26 12:33|
|Summary||0000329: FIXED: K-Means++: 'multiple restarts' doesn't work correctly|
I have a problem regarding the K-Means++ implementation contained in ALGLIB.
Please have a look at kmeans.cpp:238:
if( ap::fp_less(e,ebest) )
copymatrix(ct, 0, k-1, 0, nvars-1, ctbest, 0, k-1, 0, nvars-1);
Now, if "e" is less then "ebest", the current table containing centroids is saved as the "best centroids set", but, as you can easily see, the variable "ebest" is never updated, so its value will always be "ap::maxrealnumber". As a consequence of this, the "number of restarts" of the algorithm is completely useless, because only the last iteration will be considered, even if it's not the best one.
Am I wrong? This produces an output which is not the best one computed by the algorithm.
Yes, you are perfectly right. Thanks for bug report.
This issue will be fixed in the next release, which is scheduled for June, 1st.
|Another thing: I think you should also add something like "xyc_best", because at this time the "xyc" vector is overwritten at every iteration, and so only the last one is reported as output, and that's not good for the same initial reason.|
* issue is fixed in 2.6.0
* added unit test which checks for statistically significant difference between Restarts=1 and Restarts>1 (solution qualities are compared).
|2010-05-07 22:52||gighi||New Issue|
|2010-05-07 22:52||gighi||Programming language||=> C++|
|2010-05-08 14:55||gighi||Issue Monitored: gighi|
|2010-05-10 23:00||SergeyB||Status||new => assigned|
|2010-05-10 23:00||SergeyB||Assigned To||=> SergeyB|
|2010-05-10 23:01||SergeyB||Note Added: 0000048|
|2010-05-10 23:02||SergeyB||Summary||K-Means++ wrong implementation => K-Means++: 'multiple restarts' doesn't work correctly|
|2010-05-14 21:42||gighi||Note Added: 0000049|
|2010-05-26 12:31||SergeyB||Summary||K-Means++: 'multiple restarts' doesn't work correctly => FIXED: K-Means++: 'multiple restarts' doesn't work correctly|
|2010-05-26 12:31||SergeyB||Programming language||C++ => Unspecified|
|2010-05-26 12:33||SergeyB||Note Added: 0000052|
|2010-05-26 12:33||SergeyB||Status||assigned => resolved|
|2010-05-26 12:33||SergeyB||Fixed in Version||=> [NOT RELEASED YET] Next release|
|2010-05-26 12:33||SergeyB||Resolution||open => fixed|
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