# Thread: terribly muddled about linear notation

1. ## terribly muddled about linear notation

I'm supposed to be working with block matrices to solve a problem but I can't visualize what I'm supposed to be looking for. The problem is B=ATA, show that bsubij=avectorsubiT times avectorsubj (sorry I don't know how to use latex). I understand matrix multiplication and what a transpose is but 1) i dont know what bsubij means (does it mean any general element in B? If so, what am I supposed to do with it?) 2) is avectorsubiT the transpose of any given row from A? If so, how is this relevant? 3) is avectorsubj any given column of a? If so, how is this relevant?

I feel that some graphical view of where such i,j elements lie would help me understand this problem a lot more. I would appreciate any help.

2. ## Re: terribly muddled about linear notation

Originally Posted by charmedquark
I'm supposed to be working with block matrices to solve a problem but I can't visualize what I'm supposed to be looking for. The problem is B=ATA, show that bsubij=avectorsubiT times avectorsubj (sorry I don't know how to use latex). I understand matrix multiplication and what a transpose is but 1) i dont know what bsubij means (does it mean any general element in B? If so, what am I supposed to do with it?) 2) is avectorsubiT the transpose of any given row from A? If so, how is this relevant? 3) is avectorsubj any given column of a? If so, how is this relevant?

I feel that some graphical view of where such i,j elements lie would help me understand this problem a lot more. I would appreciate any help.
You can use LaTeX tags
As you can see, without LaTeX your post is unreadable.
$$b_{ij}=\vec{a}_{i}T$$ gives $\displaystyle b_{ij}=\vec{a}_{i}T$.

3. ## Re: terribly muddled about linear notation

When i wrote T, I meant transpose. Is it at least possible to get help for a problem that is at least partially understood?

4. ## Re: terribly muddled about linear notation

Originally Posted by charmedquark
When i wrote T, I meant transpose. Is it at least possible to get help for a problem that is at least partially understood?
I cannot read the question.
$$B=A^{T}A$$ gives $\displaystyle B=A^{T}A$.
Why don't at least try to make more readable?

5. ## Re: terribly muddled about linear notation

What a conundrum...making it more understandable is tantamount to solving my problem...but I think when i write avectorsubi transpose, i take that to mean [asubin, asubi(n-1),...asubi1], and I think that avectorsubj=[asub1j]. Is this of any help?
[asub2j]
:
[asubmj]