# I Notation (index notation)

#### kezzstar

I am having trouble converting [D]=[A][ B]T[C] to index notation.
I initially thought it would be Dij=AijBkjCkl but I have doubts that this is correct.

Would anyone be able to elaborate on this?

Regards

#### Khashishi

Where did B come from?

#### kezzstar

Where did B come from?
BT? It is the transpose of B.

#### Khashishi

Err, did you edit your post? I didn't see a B in your equation before. Anyways, nevermind.

#### kezzstar

Err, did you edit your post? I didn't see a B in your equation before. Anyways, nevermind.
No I never editted the equation. Do you have any ideas?

#### Mark44

Mentor
Err, did you edit your post? I didn't see a B in your equation before. Anyways, nevermind.
The OP had [B], which browsers treat as the start tag for bold fonts. That screwed up the equation. I edited the equation to fix that problem.

#### Svein

I am having trouble converting [D]=[A][ B]T[C] to index notation.
OK. Let us start at the right. First: $B^{T}_{j,k}=B_{k,j}$, so $(B^{T}\circ C)_{j,l}=\sum _{k}B^{T}_{j,k}C_{k,l}$. Then inset A at the front in the same way: $A\circ (B^{T}\circ C)_{i,l}=\sum _{j}A_{i,j}(\sum _{k}B^{T}_{j,k}C_{k,l})$.

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