A few days ago I created the tag . I did not discuss this tag on meta before creating it (although I mentioned creating this tag in the Tagging chatroom). Not so long after the tag creation a post in the Tag cleanup thread about this tag was made.

My reasons for creating this tag were:

1. Although do not know anything about Kalman filter, judging simply by the fact, that I have heard it mentioned many times and also by the number of post here on MSE, it seems to be rather important topic.
2. Many people kept using as a tag for such questions. However, as stated in the tag-info, this tag is supposed to be used for filters in the set-theoretic/order-theoretic sense. I hoped that creating a separate tag could help lower the number of mistagged questions.

As I am not familiar with Kalman filtering, I was not sure what to put into the tag-excerpt/tag-wiki, so I left them empty. (If someone can volunteer write something up, it would be great.)

My main intention was to solve the problem with incorrectly tagged question. This could be also solved by making a synonym of a more general umbrella tag. However, I am not sure whether there is an appropriate general tag for this. (I suppose that users asking about Kalman filtering would notice and use it instead of . If it is made a synonym of a more general tag, (kalman-filter) will be automatically changed to the master tag.)

Perhaps the most important question, which was already raised by Asaf, is: Is this tag useful? Should we keep it?

• @gnometorule: Note that the set theoretic filters are really just order theoretic filters, applied to $\subseteq$. And for many people that would really just be a topological issue, and not a set theoretical one, since one is likely to meet filters in a topology course. – Asaf Karagila Oct 8 '14 at 17:57