Re: fem-fenics questions

[Marco Vassallo]

On Mon, Mar 3, 2014 at 8:53 AM, Daniel Kraft <address@hidden> wrote:

2) Since I do not only want to plot the result but also work with it
further, I need to evaluate the result at my grid points.  With linear
Lagrange elements, I "could" use the coefficients obtained directly, but
this is probably a bad idea from the point of view of code design.  Thus
I'm using feval now, but it is not entirely clear to me how it is
supposed to be called.  The doc only says the second argument should be
the "coordinate" of evaluation, but doesn't specify how this coordinate
should look like.  It works for me now if I pass an array of x- and
y-coordinate.  I guess this is how the function is meant to be called?

Yes, sorry if it wasn't clear. You can add an example on the wiki [1].
 

Is it also possible to invoke it for lots of points at all?  (I think I
read somewhere that this is planned but not yet implemented ... just
checking what the current state is.)  This is a very important feature,
IMHO, for everyone working seriously with the result afterwards (and not
just plotting it).

You are right, I planned to do it. The function feval() is only a wrapper to the dolfin::eval()

function. At the moment I don't know any dolfin function which could evaluate lots of points

at the same time. An easy solution would be to add a for cycle in the feval.cc function

which evaluate the function for all the points given from the user.

I think that we can do either a function with a different signature:

 
  feval ( function function_name, Array<double> x_coordinates,
             Array<double> y_coordinates, Array<double> z_coordinates)

or a function with a similar signature as the one we are using now but receiving a matrix

of points and not an array. What do you think?
If you want to implement it or you have any better idea it would be great.

Marco

Yours,
Daniel

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