rational numbers with cython
I want to work efficiently with rational numbers under the context %cython but I don`t know how. Can anyone suggest any ideas? Thank you.
An example:
%cython
def rational_partitions(n):
sol = [i/n for i in range(n)]
for a in sol[0:-1]:
for b in sol[1:]:
k=2
while abs(b-a)/k>1/n:
sol.append(abs(b-a)/k)
k += 1
return sol
rational_partitions(10)
Can you say a bit more about what you want to do? Or give some Sage code that you would like to cythonize?
I re-edited with an example. Thanks.
Note that cython does provide a limited "machine integer" type in the form of C int or C long, which behave different from python ints and sage Integers in that they silently overflow rather than use multiprecision arithmetic. Cython does NOT provide such a type for rational arithmetic because C does not provide it. When you do arithmetic with rational numbers, overflow happens remarkably easily, so having fixed bitlength rational numbers would probably not have much use anyway.
If you're finding that the python wrappers are causing undue speed loss, you can look in
sage/rings/rational.pyxandsage/rings/rational.pyxand see how much can be gained from interfacing at the C-level. Surprisingly few routines are mentioned in thepxd, but thecdef mpq_t valueattribute allows you to use the super-optimized gmpmpqroutines to compute with rational numbers.@nbruin: you could turn both of your comments into an answer.