Suggested edit:
Answer: Volume of a solid with base of circular disk, parallel crosssections perpendicular to base are squares.

I found the above linked answer a couple days ago, and thought it was helpful, so I upvoted. However, I noticed that it seemed to be rendering incorrectly, with the dx before the actual function:

enter image description here

(I did upvote; the screenshot is from an incognito window so no extensions are active)

So I suggested the linked edit, putting the dx after the integral content. However, it was rejected as superfluous, which I don't really understand. At least in Chrome 70, it doesn't look correct, and confused me when I first read it. As it is, it's not taking the integral of A(x), but rather of just 1.

I have to admit that I'm not an expert in mathematical notation, however, I didn't find anything about this on this meta, or any other posts that put dx before the integrated function.

What did I do wrong?


Thanks for the responses. I never knew that dx could go before the integrand. But from the posts Florian linked, and from what Florian said, it seems like doing that is better for nested integrals or more complex integrals, where it needs to be easier to separate the components.

Since this is a pretty basic integral, and it's probably something students will run into a lot, and since it seems like students are taught with dx going after the integrand more, I'm starting to think that it does improve readability, even if it's currently correct notation.

I could accept a "goes against the author's intent" rejection, but now the "does not improve readability" rejection makes less sense to me.

  • I agree, it looks a bit odd to put the infinitesimal cart before the horse, but it might be more appropriate to simply post a comment asking Gordon if there's any particular reason he did so. – Barry Cipra Dec 3 at 16:17
  • @BarryCipra since I didn't know it was valid notation, I figured it was just an outdated answer, where the formatting had been invalidated through updates to the site. If I had known, I probably would have commented. – TheWanderer Dec 3 at 16:18
  • Ah, I see what you mean. When you went to make the edit, however, you presumably saw the unformatted TeX code, which had the dx first. I don't think updates ever affect what people literally type. At any rate, I wouldn't worry about having the edit rejected. – Barry Cipra Dec 3 at 16:28
  • @BarryCipra I did see that, and since I have no idea how TeX works I thought maybe it used to render differently. I'm not so worried about the rejection but I want to understand it in case I suggest future edits. – TheWanderer Dec 3 at 16:29
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    The template reasons for rejection sometimes only approximate what people have in mind. In this case, someone reviewing your edit may have thought, It doesn't matter where you put the dx, so it doesn't make the answer any more readable to move it to the end. – Barry Cipra Dec 3 at 16:45
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    In keeping with the spirit of @BarryCipra's comment, when I review suggested edits, unless it improves a post non-trivially, I'll reject superficial edits as no improvement. That includes, e.g., someone who edits this line in a post: $\displaystyle \frac{dx}{dy} + y = 17$, to read $$\frac {dx}{dy} + y = 17$$ and makes no other changes than one such as that. Suggested edits need to be offered in the spirit of really improving a post. Of course, the cut off line for "what really improves a post" is going to vary from person to person, to some degree. – amWhy Dec 3 at 18:20
up vote 8 down vote accepted

It may be more common to write $\int A(x) {\rm d}x$ especially when we learn about integrals in school. Yet some disciplines prefer the notation $\int {\rm d}x A(x)$, emphasizing on the fact that $\int {\rm d}x$ can be seen as an operator that is applied to $A(x)$. This issue is discussed on MSE here and there, see for instance this question or this one.

  • Oh that's interesting. I never knew that that was another notation. But wouldn't, at least in this case, it be easier to read with the dx after A(x) and (r^2-x^2)? This is a pretty basic integral, and it's probably used more in school, right? – TheWanderer Dec 3 at 16:14
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    I think it's worth adding that this particular edit was applied to an answer that's more than 5 years old, and that hasn't been active since then. Many users will reject (even decent) minor edits to such old questions because the very minor benefit of the edit doesn't merit bumping such an old post to the front page again. – T. Bongers Dec 3 at 16:15
  • @T.Bongers I don't know the consensus here, but there have been a couple posts lately on MetaSE about trivial edits, and I got from them that it was fine to make small improvements to old questions as long as you weren't seeking them out. – TheWanderer Dec 3 at 16:16
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    @TheWanderer The culture tends to vary a bit between SE sites, and MSE is probably a bit less accepting of these things. But a lot of it is just frankly luck, depending on which reviewers look at your edit. There's nothing wrong or against a rule about these edits per se, just they'll have a much higher rejection rate than typical. – T. Bongers Dec 3 at 16:29
  • @TBongers I've been caught out by this—I wrote quite a detailed answer to what I thought was a new post, only to discover it was 2 years old. It was one of those "This is where I'm stuck in this very specific problem" questions so my answer was probably of no use whatever to anyone. – timtfj Dec 3 at 17:14

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