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I do research in matrix equations, which (at least in my field) is commonly accepted to mean "equations whose unknown is a matrix, such as an algebraic Riccati equation $A^*X+XA+Q-XGX=0$, everything square".

I see that the tag here is used instead mainly to mean "systems of linear equations", or even worse "something which involves matrices", probably by people outside the numerical linear algebra community.

I, personally, think that the correct thing to do is retagging all the questions that misuse it and add a tag excerpt to make it clearer, but first I'd like to ask for opinions here.

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    While we're at it, we also have the tags matrix and matrices, which should be (but aren't) synonyms of each other. – Christian Clason May 27 '16 at 15:45
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I think you're right that the tag should be used to mean "equations in which the unknown is a matrix", like a Sylvester equation. I support this retagging.

  • What are the accepted practices for retagging on scicomp.se? For instance, Mathoverflow frowns upon retagging more than 4-5 questions at the same time, because they don't want them to flood the main page. Is it the same here? – Federico Poloni May 28 '16 at 8:27
  • I don't think it's come up before. I don't have strong opinions either way. @Paul? – Geoff Oxberry♦ May 31 '16 at 20:39
  • @FedericoPoloni I think that's reasonable, in particular since SciComp has significantly lower traffic than MO. (I usually work my way down the list of tagged questions sorted by vote, so it's fairly obvious where I (or somebody else) stopped and I should pick up.) – Christian Clason Jun 1 '16 at 12:33
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I agree, and went ahead and created a tag excerpt to this effect (please improve where needed). I've explicitly pointed to for the alternative.

On a related note: There's about 10 questions tagged , which seems in almost all cases to be redundant (although not consistently so; some are tagged , others ). This can be remedied in the same cleanup round, but we might also wish to burninate the tag?

Edit: Actually, before going ahead, we should discuss the target tag: there's both (182 questions) and (21 questions). Do we want to pick one over the other? Make them synonyms? Treat (and document) them as different (e.g., the former is for questions about algorithms or code, the latter for questions about the mathematical properties -- that would be a massive effort, though)?

Edit 2: Thinking about this, I'd propose to deprecate in favor of : Most questions with the former have both tags anyway, and the few that are not about solvers can be retagged as .

Edit 3: I've completed retagging all (in my opinion) mistagged questions with . I can start retagging , but I'd prefer if a moderator burninate (i.e., delete and blacklist) the tag instead.

  • Probably it comes from people mistakenly typing "linear<space>something" instead of "linear<hyphen>something" when entering tags. I agree with you -- let's nuke it from orbit. – Federico Poloni May 27 '16 at 15:40
  • Thanks for taking the initiative to do this! – Geoff Oxberry♦ May 31 '16 at 20:39
  • Thanks for reminding me, I forgot to finish the last few (took a break in order not to swamp the front page)! – Christian Clason May 31 '16 at 21:29
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    Deleted all linear tags from questions, and added a description to the wiki stating the tag is deprecated. – Geoff Oxberry♦ Jun 1 '16 at 21:43

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