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[James Avery <question158285@xxxxxxxxxxxxxxxxxxxxx>]

Question #158285 on DOLFIN changed:
https://answers.launchpad.net/dolfin/+question/158285

James Avery posted a new comment:
Hi Anders,

Thanks a lot! That works. However, a quick follow-up question: It seems
to me that it should be possible to compute the derivatives of a finite-
element function f in a more efficient manner, since we have f's
expansion in terms of basis functions that can be differentiated,
although I have not been able to find out how these are accessed in
DOLFIN.

Is it strictly necessary to assemble and solve a new linear system to
obtain a gradient? The reason I'm asking is, that the bottleneck in my
application is due to the matrices describing the linear systems (with
mesh size of up to a couple million cells). Thus assembling a matrix (or
storing a precalculated one) and solving a linear system is a fairly
large operation. Is there perhaps a shortcut for just computing the
function derivatives with DOLFIN?

Thank you again for your help!

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