Calculation of the gradient

[Jundi He]

Hi Nek5000 users:

May I ask how to calculate the gradient of a variable vx, at only one direction? To calculate the gradient, I normally call subroutine gradm1:

call gradm1(dudx, dudy, dudz, vx)

But what if I only need the gradient at x direction (dudx), is there a subroutine that only calculates the gradient at one direction? Thanks!

Regards!

Jundi

[Fischer, Paul]

When you compute one, the others come for free, so there is no advantage

to computing just one.

This is because each requires application of the chain rule:

du/dx = r_x * du/dr + s_x * du/ds + t_x * du/dt

and it is the du/dr, du/ds, du/dt that is expensive.

---

From: nek...@googlegroups.com <nek...@googlegroups.com> on behalf of Jundi He <jund...@sheffield.ac.uk>
Sent: Tuesday, January 11, 2022 8:30 AM
To: Nek5000 <nek...@googlegroups.com>
Subject: [nek5000] Calculation of the gradient

 

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[Jundi He]

Hi,

Thanks for the useful information. 

Regards!

Jundi