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["Alessio Quaglino" <alessio@xxxxxx>]

I was confusing with the notation not distinguishing between S as a
function or as its coefficients. What I'm thinking is to write first the
unknowns S and u using the basis functions (indicated with the name of the
test function belonging to the same space):

S = S_coeff psi_trial
u = u_coeff phi_trial

so that we have:

A = dot(S, grad(phi)) =
= S_coeff (psi_trial, grad(phi)) =
= dot(u, psi) * (psi_trial, grad(phi)) =
= u_coeff * dot(phi_basis, psi) * (basis_psi, grad(phi))

the problem is that the two terms have first to be integrated and then
multiplied. Would that be possible?

Thanks,
Alessio


> I don't see how to do this. As I understand, you have two matrices and
> you want to compute their product. So you want to compute a sum of
> products of integrals. I don't know how to write this as a single
> integral (other than as a "double integral" over the square of the
> domain).
>
> What is the quantity you want to compute in the end? Can you write it as
> a single integral?
>
> /Anders
>
>
> Alessio Quaglino wrote:
>> I have a question about matrix multiplication in FFC. Say I want to
>> measure a certain quantity S in respect to a test function psi belonging
>> to the same finite space:
>>
>> S = dot(u, psi) (1)
>>
>> and then I want to use this measure to assemble the bilinear form where
>> phi is taken from the same finite space of u:
>>
>> A = dot(S, grad(phi)) (2)
>>
>> this is equivalent to assemble the bilinear form (1) obtaining the "m x
>> n"
>> matrix S and then the bilinear form (2) obtaining the "n x m" matrix A.
>> Then what I need is to perform the multiplication A*S getting a "n x n"
>> matrix. Can I write A in such a way that this is done directly in the
>> form? Do I have to define a trilinear form?
>>
>> Thanks,
>> Alessio Quaglino
>>
>>
>>
>>
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>