On 2013-09-27, Volker Braun <vbraun.n...@gmail.com> wrote:
> The simpler C++ stuff is now well supported in Cython. Esoteric features
> will always cause troubles, but just using the std library is easy. Have a
> look at sage/tests/stl_vector.pyx for an example.
there is the line
mpz_add_ui(accumulator.value, accumulator.value, <int>(i[0]))
in the loop:
cdef Integer accumulator = Integer(0)
cdef vector[int].iterator i = self.data.begin()
while i != self.data.end():
mpz_add_ui(accumulator.value, accumulator.value, <int>(i[0]))
i += 1
which is not clear to me:
1) why can't one just use '+' instead? Is it a cython limitation?
2) why i[0] ?
Dima
>
>
>
>
>
> On Friday, September 27, 2013 5:00:07 PM UTC+1, mmarco wrote:
>>
>> I thought that C was easyer to interface from cython than C++
>>
>> Anyways, the solution of passing the length of the array and then copying
>> the values one by one doesn't sound bad to me.
>>
>> El jueves, 26 de septiembre de 2013 15:28:37 UTC+2, Volker Braun escribió:
>>>
>>> Numpy only does machine datatypes and python objects. You can do a numpy
>>> array of python wrappers of mpfr reals but that would not be a good
>>> solution here.
>>>
>>> If the library is under your own control, I would recommend to use C++
>>> instead of C and then design the interface around std::vector<double>. This
>>> is easier than C arrays, and more easily wrapped in Cython as well.
>>>
>>>
>>> On Thursday, September 26, 2013 2:14:29 PM UTC+1, Dima Pasechnik wrote:
>>>>
>>>> On 2013-09-25, Volker Braun <vbrau...@gmail.com> wrote:
>>>> > A pointer to a dynamically malloc'ed array doesn't know how long the
>>>> array
>>>> > is. Your C library function must returns its size, too. You can then
>>>> read
>>>> > it out one-by-one but you can't call list(c_array) since the latter
>>>> doesn't
>>>> > even know how long it is.
>>>>
>>>> I read somewhere that it is convenient to use numpy arrays in such
>>>> a situation (they are stored intrenally as C arrays, and there are extra
>>>> Python hooks kept by numpy).
>>>> Not sure I can reproduce details here.
>>>>
>>>> >
>>>> >
>>>> >
>>>> > On Wednesday, September 25, 2013 5:02:55 PM UTC+1, mmarco wrote:
>>>> >>
>>>> >> I see, thanks.
>>>> >>
>>>> >> So, if i understand it correctly, i import my_c_function and then, to
>>>> call
>>>> >> it, i create the memory space for the array, copy the data into it
>>>> and pass
>>>> >> the array to the function.
>>>> >>
>>>> >> I guess the result will be another c array that i can access from
>>>> python
>>>> >> in a transparent way, right?
>>>> >>
>>>> >> I mean, if i write:
>>>> >>
>>>> >> res=my_c_function(c_values)
>>>> >>
>>>> >> Then i can just use
>>>> >>
>>>> >> list(res)
>>>> >>
>>>> >> to get a list of floats?
>>>> >>
>>>> >>
>>>> >> El miércoles, 25 de septiembre de 2013 13:22:51 UTC+2, Volker Braun
>>>> >> escribió:
>>>> >>>
>>>> >>> Definitely use Cython.
>>>> >>>
>>>> >>> For array of doubles, say, you just need a sage/libs/my_library.pyx
>>>> with
>>>> >>>
>>>> >>> include "stdsage.pxi"
>>>> >>>
>>>> >>> cdef extern from "my_library.h"
>>>> >>> my_c_function(double*)
>>>> >>>
>>>> >>> def my_python_function(values):
>>>> >>> cdef double * c_values = <double*>
>>>> >>> sage_malloc(sizeof(double)*len(values))
>>>> >>> for i,v in enumerate(values):
>>>> >>> c_values[i] = values[i]
>>>> >>> my_c_function(c_values)
>>>> >>>
>>>> >>>
>>>> >>>
>>>> >>>
>>>> >>>
>>>> >>>
>>>> >>> On Wednesday, September 25, 2013 10:08:24 AM UTC+1, mmarco wrote:
>>>> >>>>
>>>> >>>> We are working on a c library to do homotoy continuation of
>>>> polynomial
>>>> >>>> roots using interval arithmetic. Our idea is to make a spkg with
>>>> it, and
>>>> >>>> write some functions in the sage library that would use it (in
>>>> particular,
>>>> >>>> to compute the fundamental group of the complement of an algebraic
>>>> curve).
>>>> >>>> so i have a question:
>>>> >>>>
>>>> >>>> how should we pass the data to the library, and retrieve it back?
>>>> Both
>>>> >>>> the input and output can be seen as an array of mpfr reals (or,
>>>> depending
>>>> >>>> on the version, floats or doubles). The length of the arrays is not
>>>> known a
>>>> >>>> priori.
>>>> >>>>
>>>> >>>> Which should be the best way to go? Write our interface in cython?
>>>> or
>>>> >>>> use ctypes? And in any case, is there some easy tutorial that we
>>>> could
>>>> >>>> follow?
>>>> >>>>
>>>> >>>> Thanks in advance.
>>>> >>>>
>>>> >>>
>>>> >
>>>>
>>>>
>
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