[petsc-users] Efficient computation of A'*A

[Jed Brown]

On Wed, Jun 15, 2011 at 19:35, Alexander Grayver <agrayver at gfz-potsdam.de>wrote:

> Actually, I'm going to use this product as a part of the following
> expressions:
>
> v'*A'*A*v
>
A'*A*v
>

Two choices here

w = A*v
result1 = norm(w)
result2 = A'*w

preprocess: B = A'*A
w = B*v
result1 = dot(v,w)
result2 = w


Note that B will require a bit more storage it is less sparse. It is
probably problem-dependent which of these is faster.
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