On 17/12/08 05:11 AM, Johan Hake wrote:
On Tuesday 16 December 2008 23:30:17 Bartosz Sawicki wrote:
On 16/12/08 03:04 PM, Garth N. Wells wrote:
Bartosz Sawicki wrote:
Before the function revolution there was method cell() inside the
Function. I used it to determine index of current cell during assembly
procedures, in eval() method. I realized that it disappeared now.
How similar functionality can be achieved today?
You'll need to use the eval variant
void eval(double* values, const Data& data) const;
and you can then access the cell via
const Cell& cell = data.cell();
Thanks. That's clear now.
Remember that corresponding section of the manual needs to be updated.
That is probably true, together with a lot of other stuff... :)
Do you plan to extend python interface to follow this changes?
The pure python interface only support values and x as arguments to the
callback function eval(). It should probably be possible to expose the
data structure to python too, but this wont be a priority right now.
You can always define your own C++ function and compile it in python.
cppcode = '''
class MyFunc : public Function
{
public:
MyFunc(FunctionSpace& V) : Function(V) {}
void eval(double* values, const Data& data)
{
// write your C++ code here!
}
};'''
my_func = Function(V,cppcode)
my_func can then be used in form formulation, and then automaticly used
in the assembly too. Unfortunatly you cannot use this function directly
from the python prompt, i.e.
my_func.eval(v,x)
wont work, as the data structure is created duing assemble.
Btw, with the new Function interface we have made it much easier to use
compiled c++ function from python. Have a look in the docstring of
Function. I strongly encourage you to use compiled function instead of
pure python functions as the performance boost is significant during
assemble.
Thank you for explanation. I've just tried tried to apply this, but I
failed.
Please have a look into this simple example:
u = Function("poisson.xml")
mesh = u.function_space().mesh()
Vv = VectorFunctionSpace(mesh, "Discontinuous Lagrange", 0)
cppcode = '''
class MyFunc : public Function
{
public:
MyFunc(FunctionSpace& V) : Function(V) {}
void eval(double* values, const Data& data){
values[0] = 1.0;
}
};
'''
v = TestFunction(Vv)
E = TrialFunction(Vv)
mat = Function(Vv, cppcode)
a = dot(v,E)*dx
L = -mat[0]*dot(v,grad(u))*dx
pde = LinearPDE(a, L)
E = pde.solve()
And error message:
Ordering mesh (finished).
Creating linear PDE with 0 boundary condition(s).
Solving linear PDE.
Assembling matrix over cells (finished).
Assembling vector over cells (finished).
Traceback (most recent call last):
File "grad.py", line 41, in <module>
E = pde.solve()
File
"/home/sawickib/dolfin/local/lib/python2.5/site-packages/dolfin/pde.py",
line 54, in solve
cpp.LinearPDE.solve(self, u)
File
"/home/sawickib/dolfin/local/lib/python2.5/site-packages/dolfin/cpp.py",
line 10908, in solve
return _cpp.LinearPDE_solve(*args)
RuntimeError: *** Error: Missing eval() for user-defined function
(must be overloaded).
Error message is a little bit strange for me. Why it doesn't see eval()
function?
