[Examples] Potential mismatch between equation and Kernel variable in ex03_coupling

[Daybyday-there]

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Question

I am a beginner in MOOSE. Recently, I came across some tutorials and examples. While examining example 3 (https://mooseframework.inl.gov/releases/moose/2024-11-11/getting_started/examples_and_tutorials/examples/ex03_coupling.html), I noticed that the kernel settings in the input file (ex03.i) seemed to be inconsistent with the physical equations stated in the problem description. According to the document, the equation of this example is:
$-\nabla\cdot\nabla u + \nabla v \cdot \nabla u = 0$，
$-\nabla\cdot\nabla v = 0$，
and the document states that the variable diffused corresponds to the physical variable $u$, and the variable convected corresponds to the physical variable $v$.
However, In the [Kernels] of ex03.i:
[./conv]
type = ExampleConvection
variable = convected
some_variable = diffused
[../]
This kernel acts on the convected (i.e., the physical variable $v$) equation, but the physical equation requires that the coupling term $\nabla v \cdot \nabla u$ should act on the equation of $u$.

[GiudGiud]

Hello

and the document states that the variable diffused corresponds to the physical variable $u$,

This would be the problem, u is convected here, and v is diffused.
I'm struggling to locate that statement on the page, if you can paste the document's statement I could go fix it

Thanks for engaging on this,
Guillaume

[Daybyday-there]

Sorry for the late reply. There are many areas that need to be revised, for instance, in the second paragraph under the "Input File Syntax" section, it states: "Then, the two variables are defined: 'diffused' and 'convected', which refer to u and v from the problem statement, respectively." In the BCs block definition of ex03.i, the [value] in [bottom_convected] and [bottom_diffused] should be swapped. The titles and legends of Figures 1 and 2 also need to be swapped, which might be a bit troublesome.

[Daybyday-there]

However, there is a simpler method, which is to modify the boundary conditions in example 3.

The above boundary conditions can be changed to "u = 1 and v = 2 on the bottom boundary."

[GiudGiud]

Thanks for reporting,
created #33458 to keep track of the fixing