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Rename derivative_dhat => derivative_hat, explain minus signs#2725

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DanielDoehring merged 28 commits intotrixi-framework:mainfrom
DanielDoehring:ExplainDHat
Jan 18, 2026
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Rename derivative_dhat => derivative_hat, explain minus signs#2725
DanielDoehring merged 28 commits intotrixi-framework:mainfrom
DanielDoehring:ExplainDHat

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@DanielDoehring DanielDoehring commented Jan 6, 2026

$D$ is the abbreviation for the derivative matrix, so derivative_dhat is somewhat doubled - we also do not have derivative_dsplit but only derivative_split:

Trixi.jl/src/solvers/dgsem/basis_lobatto_legendre.jl

Lines 30 to 33 in b08f7da

derivative_matrix::DerivativeMatrix # strong form derivative matrix
derivative_split::DerivativeMatrix # strong form derivative matrix minus boundary terms
derivative_split_transpose::DerivativeMatrix # transpose of `derivative_split`
derivative_dhat::DerivativeMatrix # weak form matrix "dhat",

Furthermore, I compressed boundary_interpolation to the only two retrieved values. I think this is fine since the stored boundary matrix is currently also not the full one.

I also added a couple comments on the (minus)-sign in the construction of the matrices.

@DanielDoehring DanielDoehring added low-priority refactoring Refactoring code without functional changes labels Jan 6, 2026
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github-actions bot commented Jan 6, 2026

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codecov bot commented Jan 6, 2026 •
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Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 97.02%. Comparing base (19f769d) to head (15cdf0c).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files 
@@           Coverage Diff           @@
##             main    #2725   +/-   ##
=======================================
  Coverage   97.02%   97.02%           
=======================================
  Files         563      563           
  Lines       44222    44225    +3     
=======================================
+ Hits        42904    42907    +3     
  Misses       1318     1318
Flag Coverage Δ
unittests 97.02% <100.00%> (+<0.01%) ⬆️

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jlchan
jlchan requested changes Jan 16, 2026
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DanielDoehring commented Jan 16, 2026

@jlchan we can also postpone the boundary stuff and just focus on the derivative matrix (as the title suggests 🙊 )

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I'm OK with the Dhat change if you want to just do that refactoring first. It might also be good to get one more review since this PR touches a lot of code

@DanielDoehring DanielDoehring changed the title Rename derivative_dhat => derivative_hat Rename derivative_dhat => derivative_hat, explain minus signs Jan 17, 2026
@DanielDoehring DanielDoehring requested a review from jlchan January 17, 2026 00:19
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Thanks for removing the boundary stuff. One minor comment on your comment

@DanielDoehring DanielDoehring requested a review from jlchan January 17, 2026 19:24
@DanielDoehring DanielDoehring merged commit 123b8b1 into trixi-framework:main Jan 18, 2026
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@DanielDoehring DanielDoehring deleted the ExplainDHat branch January 18, 2026 08:48
@DanielDoehring DanielDoehring mentioned this pull request Jan 18, 2026
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ranocha
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src/solvers/dgsem_p4est/dg_2d_parabolic.jl
Comment on lines 967 to 969

# Access the factors only once before beginning the loop to increase performance.
# We also use explicit assignments instead of `+=` to let `@muladd` turn these
# into FMAs (see comment at the top of the file).
factor_1 = boundary_interpolation[1, 1]
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@ranocha ranocha Jan 18, 2026

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Why did you remove this comment?

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@DanielDoehring DanielDoehring Jan 18, 2026 •
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I found that improvement pretty trivial/obvious. And to prevent comment overload decided to remove that.

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I found that pretty trivial/obvious improvement and to prevent comment overload decided to remove that

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@ranocha ranocha Jan 18, 2026

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Ok, thanks

This was referenced Jan 19, 2026
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DanielDoehring added a commit to DanielDoehring/Trixi.jl that referenced this pull request Feb 19, 2026
@DanielDoehring
Rename derivative_dhat => derivative_hat, explain minus signs (tr…
9f66737 
…ixi-framework#2725)

* explain dhat

* comment boundary matrix

* comments

* rev

* comments

* rename

* comment

* comments

* update

* comment

* compress boundary matrix

* rev

* rm comment

* revert boundary stuff

* rev

* fix

* rm comment

* comments

* comment
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