Defining _Dcomplex externally in Cython

To define _Dcomplex externally in Cython, you can use the extern keyword in the Cython code to indicate that the variable is defined externally. Here's an example:

1. Create a complex_def.h header file with the definition of _Dcomplex. For example:

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typedef struct {

    double real;

    double imag;

} _Dcomplex;

1. In your Cython code, import the complex_def.h file and declare _Dcomplex as an external variable. For example:

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cdef extern from "complex_def.h":

    ctypedef struct _Dcomplex:

        double real

        double imag



# Now you can use _Dcomplex in your Cython code

cdef _Dcomplex my_complex

1. Compile your Cython code, making sure to include the complex_def.h file in the compilation process. For example:

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cython my_module.pyx

gcc -shared -o my_module.so my_module.c -I/path/to/header/files

Make sure to replace /path/to/header/files with the actual path to the directory containing complex_def.h.

With this approach, you can define _Dcomplex externally in the complex_def.h header file and use it in your Cython code by including the header and declaring it as an external variable.