2-point correlation functions
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**cBalls** can compute 2-point correlations (2pcf) when counts (N) or a scalar field are involved (like convergence K):

:NN:  It is the normal 2-point correlation function of number counts (typically
      galaxy counts).

:KK:  So far we have consider that the scalar field is the convergence in weak lensing :math:`\kappa`. Then this gives the 2-point kappa-kappa correlation function.

N represent simple counting and K represent a real scalar field, like convergence in weak lensing.