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Re: [Question #159771]: Derivative of Expression

To: dolfin@xxxxxxxxxxxxxxxxxxx
From: Johan Hake <question159771@xxxxxxxxxxxxxxxxxxxxx>
Date: Tue, 31 May 2011 16:55:50 -0000
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Question #159771 on DOLFIN changed:
https://answers.launchpad.net/dolfin/+question/159771

    Status: Open => Answered

Johan Hake proposed the following answer:
On Tuesday May 31 2011 09:41:18 Praveen C wrote:
> Question #159771 on DOLFIN changed:
> https://answers.launchpad.net/dolfin/+question/159771
> 
> Praveen C gave more information on the question:
> I know I can interpolate and Expression and then take grad. But I am
> looking to see if there is some automatic differentiation of an
> Expression available in dolfin.

No. The expression is only evaluated during an assemble. You need to project 
the grad of your expression to get the derivatives.

  der = project(grad(e), V)

where V is the space you would like to project your function into.

Johan

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