Add constructor of PERK3

[warisa-r]

No description provided.

[github-actions]

Review checklist

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Created with ❤️ by the Trixi.jl community.

[DanielDoehring]

Thanks a lot! I left some minor comments going beyond pure functionality.

[DanielDoehring]

Thanks Warisa! Couple more requested changes related to the comments. Note that in Trixi we use a whitespace after the comment escape symbol: # .

[DanielDoehring]

Thanks Warisa!