On 18/12/08 12:45 AM, Johan Hake wrote:
> On Thursday 18 December 2008 00:08:52 Bartosz Sawicki wrote:
>> 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?
>
> You need to make it const. This is my fault. I never tested that the
> functions
> in the docstring example actually could be assembled. I will update the
> docstring accordingly.
You was right, after adding const to the eval function, the problem
disappeared.
> Thanks for testing this out for us BArtek!
You are welcome :)
regrd.
BArtek
>
> Johan
>
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