The result was delete. There is consensus that this is not a notable topic on its own as it is not adequately covered in reliable sources. – bradv🍁 20:20, 28 March 2020 (UTC)
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I have collapsed the rationale for AfD nomination by Createangelos, and the discussion with Smithpith, who is !voting keep, because these posts are very long, and very technical. It follows that, without collapsing, non-specialists must scroll several screens before finding the core discussion based on Wikipedia rules. D.Lazard (talk) 17:24, 18 March 2020 (UTC)
Rationale for AfD nomination by Createangelos, and discussion with Smithpith, who is !voting keep
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The justification for the existence of this Wikipedia article is articles which refer to it, such as Florack, Luc; Van Assen, Hans (2011). "Multiplicative Calculus in Biomedical Image Analysis". Journal of Mathematical Imaging and Vision. 42: 64–75. doi:10.1007/s10851-011-0275-1. That article, on the second page, says It is not difficult to show that ... ln f*(x) = (ln f)'(x) This can be taken as the definition of *. This is indeed a correct formula for the action of the operator d/dx when y=f(x) if we use u=ln(y) as a coordinate. But even here it is written in idiosyncratic notation. The normal, and very very old, way to write the action of d/dx on f(x) coming from its action on ln(f(x)) is to write write ln*(d/dx)(f). That is to say, differentiation by x is pulled back via the function ln before you apply it to f. There are many references to many standard calculus texts which explain this, and physicists' notion of how vector fields (which they call 'covariant tensors of rank one') 'tranform' when you change variable. Such as page 28 of the book 'The very basic theory of tensors.' The theory of manifolds is even more general, and describes tangent fields without needing to choose *any* coordinate. An existing Wikipedia article vector field already describes this, "This representation of a vector field depends on the coordinate system, and there is a well-defined transformation law in passing from one coordinate system to the other." If someone wants to improve Wikipedia's treatment of the subject, someone can insert the formula there where it is needed. The article of Florak and Van Assen does exist, but despite the title, the article does not, and could not, make any substantial use of a notion that 'multiplicative calculus' is any different than ordinary calculus. Because ordinary calculus already subsumes 'multiplicative calculus.' Except in a few textbooks, the real line which occurs as the domain of single variable functions does not have any operation of multiplication *or* addition. It has a smooth structure only. The distinction between 'multipicative' versus 'additive' calculus is nonexistent except with reference to expository texts which make the simplifying assumption that the actual real *number line* happens to be the domain of single-variable functions; and the publication in reference [4] could not possibly be notable. Just because a research article is published and refers to something does not make that thing notable. Wikipedia does not have an encyclopaedic command of all strains of astrology, for example. The notion that there is such a separate subject as 'multiplicative calculus' which is any different than ordinary calculus would rest on the idea that *whatever* variable y one is tempted to use, it is always better (or different) to use ln(y) instead. If I can give an analogy, suppose I say, addition is good, but some numbers have no predecessor, so I am going to define "augmented addition" which is defined by saying x*y + 1 = (x+1) + (y+1) Then we see x*y = x+y+1 and we can think of this as adding the successors. Well, I've only conjugated ordinary addition by the successor function. In the case of 'multiplicative calculus' which recommends using log(y) in place of y, the process could of course be repeated, one could say, it is always better to use log(log(y)) and so-on. It is like calling functions 'logarithmic functions' which are of the form ln o f and insisting that you need a whole separate theory about 'logarithmic functions.' Seriously, it is like the theory of elements of groups which are preceded by the inverse of some other element. It is not a subject. And if articles were published by referring in a complimentary way to the subject, it is just either sad or a corrupt use of the refereeing process. Not that the originators of 'multiplicative calculus' would be to blame, but just vulnerable. Sadly, also, in situations like this, there is the possibility that the only reason such references were ever published is because an article only needs one referee to be accepted, and editors are not always conversant with the subjects of articles in their journals. As a postscript, the notion that 'multiplicative calculus' is 'scale invariant' is prejudiced by a particular notion of what should be the group of scale transformations. This whole subject was clarified beginning with work of Cartan, described here for instance http://www-math.mit.edu/~helgason/Paper45.pdf, and the algebra of vector-fields invariant under a group of transformations is an existing and very old subject, including symmetries that are not required to commute, and which have various physical interpetations. Createangelos (talk) 19:54, 17 March 2020 (UTC)
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