Using c++ complex functions in Cython - c++

Question

I am trying to do a complex exponential in Cython.
I have been able to cobble together the following code for my pyx:
from libc.math cimport sin, cos, acos, exp, sqrt, fabs, M_PI, floor, ceil
cdef extern from "complex.h":
double complex cexp(double complex z)
import numpy as np
cimport numpy as np
import cython
from cython.parallel cimport prange, parallel
def try_cexp():
cdef:
double complex rr1
double complex rr2
rr1 = 1j
rr2 = 2j
print(rr1*rr2)
#print(cexp(rr1))
Note that the print(cexp(rr1)) is commented. When the line is active, I get the following error when running setup.py:
error: command 'C:\\WinPYthon\\Winpython-64bit-3.4.3.6\\python-3.4.3.amd64\\scripts\\gcc.exe' failed with exit status 1
Note that when cexp is commented out, everything runs expected... I can run setup.py, and when I test the function it prints out the product of the two complex numbers.
Here is my setup.py file. Note that it includes code to run openmp in Cython using g++:
from distutils.core import setup
from Cython.Build import cythonize
from distutils.extension import Extension
from Cython.Distutils import build_ext
import numpy as np
import os
os.environ["CC"] = "g++-4.7"
os.environ["CXX"] = "g++-4.7"
# These were added based on some examples I had seen of cexp in Cython. No effect.
#import pyximport
#pyximport.install(reload_support=True)
ext_modules = [
Extension('complex_test',
['complex_test.pyx'],
language="c++",
extra_compile_args=['-fopenmp'],
extra_link_args=['-fopenmp', '-lm']) # Note that '-lm' was
# added due to an example where someone mentioned g++ required
# this. Same results with and without it.
]
setup(
name='complex_test',
cmdclass={'build_ext': build_ext},
ext_modules=ext_modules,
include_dirs=[np.get_include()]
)
Ultimately my goal is to speed up a calcualtion that looks like k*exp(z), where k and z are complex. Currently I am using Numerical expressions, however that has a large memory overhead, and I believe that it's possible to optimize further than it can.
Thank you for your help.

Answer 1

You're using cexp instead of exp as it is in C++. Change your cdef extern to:
cdef extern from "<complex.h>" namespace "std":
double complex exp(double complex z)
float complex exp(float complex z) # overload
and your print call to:
print(exp(rr1))
and it should work as a charm.
I know the compilation messages are lengthy, but in there you can find the error that points to the culprit:
complex_test.cpp: In function ‘PyObject* __pyx_pf_12complex_test_try_cexp(PyObject*)’:
complex_test.cpp:1270:31: error: cannot convert ‘__pyx_t_double_complex {aka std::complex<double>}’ to ‘__complex__ double’ for argument ‘1’ to ‘__complex__ double cexp(__complex__ double)’
__pyx_t_3 = cexp(__pyx_v_rr1);
It's messy, but you can see the cause. *You're supplying a C++ defined type (__pyx_t_double_complex in Cython Jargon) to a C function which expects a different type (__complex__ double).