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This article is absolute garbage. Someone needs to fix it before it gets taken down. Dr. Universe (talk) 10:52, 16 January 2010 (UTC)[reply]

Would you care to be more specific? Charles Matthews (talk) 11:28, 16 January 2010 (UTC)[reply]

@Charles Matthews: Maybe if you pinged me when I wrote that 11.5 years ago, I would have been very happy to be more specific! It's a bit too late for that now though since I don't remember :) Dr. Universe (talk) 02:03, 28 May 2021 (UTC)[reply]

I removed the garbage, and left something thin and pathetic in it's place. linas (talk) 18:26, 3 April 2026 (UTC)[reply]

This article seems to be disjointed, jumping from generic to specific examples with little warning and mostly avoiding describing what functional calculus actually is.116.90.140.41 (talk) 23:55, 28 February 2017 (UTC)[reply]

Any article that uses the phrase "If M is an operator" in the introductory section with no explanation of what the word "operator" (which has many, many meanings in English) means ... needs serious work.

(Regardless of the fact that a mathematically sophisticated reader might be able to almost figure it out.) 2600:1700:E1C0:F340:4C85:FDC4:21FA:39B8 (talk) 22:29, 9 July 2018 (UTC)[reply]

See comments above. I removed the garbage, but did not leave anything more accessible. You'll have to wait for someone else to do that. linas (talk) 18:28, 3 April 2026 (UTC)[reply]

> If f is a function, say a numerical function of a real number, and M is an operator,

What is an operator?

> there is no particular reason why the expression f(M) should make sense.

Why should we expect it to make sense? This statement would be no less meaningless if one replaced "operator" with "banana" or "shade of blue".

> If it does, then we are no longer using f on its original function domain. In the tradition of operational calculus, algebraic expressions in operators are handled irrespective of their meaning. This passes nearly unnoticed if we talk about 'squaring a matrix', though, which is the case of f(x)=x2 and M an n×n matrix.

"This passes unnoticed", and indeed, much of the article seems weirdly pompously conversational. jon (talk) 20:17, 20 January 2025 (UTC)[reply]

I removed all of these sentences. They were garbage. What's left is quite thin, though. linas (talk) 18:30, 3 April 2026 (UTC)[reply]