Problem description
See thread below and the follow up on the discussion page for more details (where the problem statements are)
How to reproduce
look at the documentation example
look at the input and figures
Impact
confusion documentation
Discussed in #33455
Originally posted by Daybyday-there July 29, 2026
Check these boxes if you have followed the posting rules.
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 $u$.
Problem description
See thread below and the follow up on the discussion page for more details (where the problem statements are)
How to reproduce
look at the documentation example
look at the input and figures
Impact
confusion documentation
Discussed in #33455
Originally posted by Daybyday-there July 29, 2026
Check these boxes if you have followed the posting rules.
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 (
$-\nabla\cdot\nabla u + \nabla v \cdot \nabla u = 0$ ，
$-\nabla\cdot\nabla v = 0$ ，$v$ ) equation, but the physical equation requires that the coupling term $\nabla v \cdot \nabla u$ should act on the equation of $u$ .
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:and the document states that the variable
diffusedcorresponds to the physical variable$u$, and the variableconvectedcorresponds to the physical variable$v$.However, In the
[Kernels]ofex03.i:[./conv]
type = ExampleConvection
variable = convected
some_variable = diffused
[../]
This kernel acts on the convected (i.e., the physical variable