dolfin team mailing list archive

[Anders Logg <logg@xxxxxxxxx>]

Anders Logg wrote:
> There seems to be more than one problem here...
>
> 1. You need to allocate the array as
>
>      real* xx = new real[3*mesh.numVertices()];
>
> 2. Yes indeed, the size is never computed and it needs to be computed 
> correctly or otherwise you'll most likely get a segmentation fault.
>
> For this to work, a user-defined function must know the dimensions of 
> the value type and it currently has no idea... I suggest we make the
> two functions dim() and rank() in Function virtual so that it is 
> possible to compute this. Any further thoughts?
>
> /Anders
>
>
> Jake Ostien wrote:
> > Hi,
> >
> > I may have found a bug in the interpolation method for the 
> > UserFunction.  In the private data there is a uint size that gets 
> > initialized to 1 in the constructor, but, as near as I can tell, does 
> > not get set anywhere else.  When I try and do something like
> >    
> >    
> >     <f is a member of a BodyForce class that returns a 3D force vector 
> > and is derived from Function, thus its a UserFunction>
> >    
> >     real* xx = new real[mesh.numVertices];
> >     f.interpolate(xx);
> >
> >
> > I get a memory error from glibc.  To make a long (painful) story 
> > short(er), I realized that in the interpolation function, local_values 
> > was of size 1 and needed to be of size 3.  So I hard coded in a 3 in 
> > place of size, and things magically got better.  Unfortunately, it is 
> > not clear to me how to fix this in the general case.  If anyone has a 
> > suggestion, I'd be happy to try it out.
> >
> > -Jake
> > _______________________________________________
> > DOLFIN-dev mailing list
> > DOLFIN-dev@xxxxxxxxxx
> > http://www.fenics.org/mailman/listinfo/dolfin-dev
> _______________________________________________
> DOLFIN-dev mailing list
> DOLFIN-dev@xxxxxxxxxx
> http://www.fenics.org/mailman/listinfo/dolfin-dev

This should be fixed now. rank() and dim() may now be overloaded.
Here's an example:

from dolfin import *

class MyFunction(Function):
    def __init__(self, mesh):
        Function.__init__(self, mesh)
    def rank(self):
        return 1
    def dim(self, i):
        return 2
    def eval(self, values, x):
        values[0] = -x[1]
        values[1] = x[0]

mesh = UnitSquare(16, 16)
f = MyFunction(mesh)

plot(f)

/Anders