I just realised that my question has been tagged off-topic and closed. Could please somebody let me know why? From my point of view, the question is quite clear, relevant and to the point.
Edit: screen-shots of the question:
Your question is closed as 'off-topic' but there might actually be multiple reasons. The SE software only lists one of them. As you should already know (after reading the help page about off-topic posts) cross-posting is classified among the off-topic category. It is possible that your question initially obtained close votes for that reason and later on for the other reasons.
To me your question 'how to verify clustering algorithms' is rather broad and more like a topic to write an entire book about rather than a question.
It has some similarity with self-study questions where we wish to see your own research effort which helps to focus the answering on the culprit rather than writing very lengthy answers (and avoiding xy problems)
You seem to be asking for help with understanding some article (it is always better to quote some exact passage where you have the problem) but it is unclear (and not to the point) what the culprit is.
Your question might be reopened given that the original close reason 'cross-posting/off-topic' is solved. However, calling people unprofessional in comments is a bit uncalled for and I imagine that you do not get a lot of people on your side to dig through your question, which is not so great based on other grounds as well, and write an answer for you.