4 ms·

This paper has a pretty major typo in Eqn 11, which started giving me flashbacks to undergrad physics where authors would make major leaps in a derivation with

This paper has a pretty major typo in Eqn 11, which started giving me flashbacks to undergrad physics where authors would make major leaps in a derivation with a one sentence explanation. Section II c tries to explain “the relationship between concavity and force” and concludes with: > Then, adding a proportionality constant k and using dimensional analysis, we arrive at d2y/dx2 = v^2 d2y/dt2 > which is the 1D wave equation .. except dimensional analysis would say that equation has m^-1 = m^3 / s^4 .. which makes no sense, until you realize they flipped dx and dt, and that isn’t actually the 1D wave equation. Although to be fair, correcting author’s typos in textbooks was one of the more educational parts of undergrad for me, so maybe that’s secretly the point of the paper.

kwhitefoot 3y ago
There is no excuse for that sort of thing these days when computational tools such as Maxima exist to check the dimensional consistency of equations.
- cinntaile 3y ago
  I can't find the homepage for Maxima?
  - jxf 3y ago
    It's here: https://maxima.sourceforge.io/project.html https://maxima.sourceforge.io/project.html
- forgotpwd16 3y ago
  There wouldn't if the computer algebra step was integrated in the typesetting. Rather you first derive/verify the equations in a CAS and then write them in TeX for the paper. Even if export (like Mathematica) you may still decide to fix formatting a bit doing a seemingly obvious change which ends up changing the expression.
  - kwhitefoot 3y ago
    A seemingly obvious change like moving a term from one side of the equation to the other?
Modified3019 3y ago
It's beyond my current ability to evaluate if there's an error, but if so good catch. The contacts for the authors are on the following linked pages, I'm sure they'd appreciate correcting a mistake sooner than later. https://www.ind.ku.dk/english/staff-auto-list/?pure=en%2Fpersons%2Fricardo-avelar-sotomaior-karam(df4e0a2f-5798-413b-a535-c0c10067b769)%2Fpublications.html https://www.ind.ku.dk/english/staff-auto-list/?pure=en%2Fper... https://research.ku.dk/search/result/?pure=en%2Fpersons%2Fmuhammad-aswin-rangkuti(37594e39-cb99-4910-9b19-538e67f26723)%2Fpublications.html https://research.ku.dk/search/result/?pure=en%2Fpersons%2Fmu...
- bee_rider 3y ago
  Dimensional analysis just means checking that the units work out. You can do it! x, dx, y and dy have units of length. dt has units of time. v, I’m guessing is velocity, so length/time. length/length^2 = (length/time)^2 * length/time^2 -> 1/length = length^3/time^4 These are different types of things, they can’t be equal to each other. It is essentially like static types in programming, but for physicists, and it is a similarly simple but dramatically powerful idea.
deleted 3y ago
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pdonis 3y ago
> This paper has a pretty major typo in Eqn 11 Yes, the v^2 should be on the other side, as it is in Eqn 5.

kwhitefoot 3y ago

There is no excuse for that sort of thing these days when computational tools such as Maxima exist to check the dimensional consistency of equations.

cinntaile 3y ago
I can't find the homepage for Maxima?
- jxf 3y ago
  It's here: https://maxima.sourceforge.io/project.html https://maxima.sourceforge.io/project.html
forgotpwd16 3y ago
There wouldn't if the computer algebra step was integrated in the typesetting. Rather you first derive/verify the equations in a CAS and then write them in TeX for the paper. Even if export (like Mathematica) you may still decide to fix formatting a bit doing a seemingly obvious change which ends up changing the expression.
- kwhitefoot 3y ago
  A seemingly obvious change like moving a term from one side of the equation to the other?

Modified3019 3y ago

It's beyond my current ability to evaluate if there's an error, but if so good catch. The contacts for the authors are on the following linked pages, I'm sure they'd appreciate correcting a mistake sooner than later. https://www.ind.ku.dk/english/staff-auto-list/?pure=en%2Fpersons%2Fricardo-avelar-sotomaior-karam(df4e0a2f-5798-413b-a535-c0c10067b769)%2Fpublications.html https://www.ind.ku.dk/english/staff-auto-list/?pure=en%2Fper... https://research.ku.dk/search/result/?pure=en%2Fpersons%2Fmuhammad-aswin-rangkuti(37594e39-cb99-4910-9b19-538e67f26723)%2Fpublications.html https://research.ku.dk/search/result/?pure=en%2Fpersons%2Fmu...

bee_rider 3y ago
Dimensional analysis just means checking that the units work out. You can do it! x, dx, y and dy have units of length. dt has units of time. v, I’m guessing is velocity, so length/time. length/length^2 = (length/time)^2 * length/time^2 -> 1/length = length^3/time^4 These are different types of things, they can’t be equal to each other. It is essentially like static types in programming, but for physicists, and it is a similarly simple but dramatically powerful idea.

deleted 3y ago

[deleted]

pdonis 3y ago

> This paper has a pretty major typo in Eqn 11 Yes, the v^2 should be on the other side, as it is in Eqn 5.