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I know what 'formal' usually means in a mathematical context, as in a formal proof or definition but I've never heard it being used to describe matrices. I couldn't find any explanation of this online. Any help would be much appreciated.

Flose
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  • Where did you find this term? – Lynn Jan 18 '18 at 12:53
  • Perhaps related? https://math.stackexchange.com/questions/915012/formal-inverse-of-a-matrix-ressembling-fouriers-matrix – Clarinetist Jan 18 '18 at 12:53
  • This is used in analytic context, see this question. Ah, this is the same link as from oboist (sorry, clarinetist). – Dietrich Burde Jan 18 '18 at 12:54
  • I'm a first year maths student and found it on some homework. – Flose Jan 18 '18 at 12:54
  • @DietrichBurde Thanks for the link, but I'm still a bit confused. That post seems to be more asking how to find on rather than what one actually is. Since my knowledge about matrices is fairly limited at this point, would it just be what I would think of as the inverse normally? – Flose Jan 18 '18 at 12:59

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In algebra, formal means using letters, without any care whatsoever about whether or not what you are writing actually makes sense when you replace the letters with some actual numbers, or functions, .

Example: the formal inverse of $1-X$ is $1+X+X^2+X^3+...$, no matter what $X$ is.

Arnaud Mortier
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