%cython
import numpy

def cython_collisions(x, y, z, radius):
    num_particles = len(x)
    collisions = numpy.zeros(num_particles, dtype=numpy.bool)

    r_min = numpy.float64(4*radius**2)

    for i in range(num_particles):
        if i>0:
            d2 = numpy.power((x[i]-x[0:i]),2) \
                + numpy.power((y[i]-y[0:i]),2) \
                + numpy.power((z[i] - z[0:i]),2)
            if d2.min() < r_min:
               collisions[i] = True
           
        if i+1 < num_particles:
            d2 = numpy.power((x[i]-x[i+1:]),2) \
                + numpy.power((y[i]-y[i+1:]),2) \
                + numpy.power((z[i]-z[i+1:]),2)
            if d2.min() < r_min:
                collisions[i] = True
                
    return collisions