### Author Topic: Lec 26 #3  (Read 3437 times)

#### Kanita Khaled

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##### Lec 26 #3
« on: November 26, 2012, 01:39:31 PM »
In Lec 26, equation (3) involves "antisymmetrizing by u, w (permutting u, w and subtracting from original formula)...

What does antisymmetrizing mean? Or Permutting for that matter? I'm not sure how we move from (2) to (3) to (4)...

Can someone kindly clarify?

#### Victor Ivrii

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##### Re: Lec 26 #3
« Reply #1 on: November 26, 2012, 03:19:45 PM »
In Lec 26, equation (3) involves "antisymmetrizing by u, w (permutting u, w and subtracting from original formula)...

What does antisymmetrizing mean? Or Permutting for that matter? I'm not sure how we move from (2) to (3) to (4)...

Can someone kindly clarify?

It means that we have expression $\mathcal{P}(u,w)$ depending on $u$ and $v$. Now we consider expression $\mathcal{P}(w,u)$ so interchange $u$ and $w$.

"Symmetrizing" would mean that we consider $\mathcal{P}(u,w)+\mathcal{P}(w,u)$ (or rather divided by $2$).

"Antisymmetrizing" would mean that we consider $\mathcal{P}(u,w)-\mathcal{P}(w,u)$ (or rather divided by $2$).

#### Djirar

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##### Re: Lec 26 #3
« Reply #2 on: November 26, 2012, 04:17:35 PM »
I think that for part (3) we are supposed to take
$\mathbf{U}=\ w \nabla u$

then you take (permutting)

$\mathbf{U}=\ u \nabla w$