Dear Henrik,

J = derivative(F, u)

results in J being a Form, which is to say a symbolic representation of the Jacobian. If F is nonlinear then u will still feature in F. At this point the Jacobian isn't evaluated so it doesn't really make sense to talk about the Jacobian at u=u0.

Typing:

M = assemble(J)

evaluates the Jacobian resulting in a matrix. Whatever value the field u holds when the assemble call occurs will be the value at which the Jacobian is assembled. You can project, interpolate or assign initial values into u at any stage before calling assemble in order to cause the evaluation to occur at your choice of initial condition.

Regards,

David

On Fri, 9 Oct 2015 at 08:52 Buesing, Henrik <HBuesing@eonerc.rwth-aachen.de> wrote:

Dear Firedrakers,

I’m evaluating the Jacobian dF/du of my nonlinear function F by,

J = derivative(F,u)

This seems to evaluate with zero u: dF(0)/du.

What I would like to have is dF(u0)/du, the Jacobian evaluated at the initial conditions.

How would I do that? Thank you!

Henrik

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Dipl.-Math. Henrik Büsing

Institute for Applied Geophysics and Geothermal Energy

E.ON Energy Research Center

RWTH Aachen University

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