code: def _calc_g(cosang, stiffness=4, n_legendre_terms=50):
      """Calculate spherical spline g function between points on a sphere.
  
      Parameters
      ----------
      cosang : array-like of float, shape(n_channels, n_channels)
          cosine of angles between pairs of points on a spherical surface. This
          is equivalent to the dot product of unit vectors.
      stiffness : float
          stiffness of the spline.
      n_legendre_terms : int
          number of Legendre terms to evaluate.
  
      Returns
      -------
      G : np.ndrarray of float, shape(n_channels, n_channels)
          The G matrix.
      """
      factors = [
          (2 * n + 1)
          / (n**stiffness * (n + 1) ** stiffness * 4 * np.pi)
          for n in range(1, n_legendre_terms + 1)
      ]
      return legval(cosang, [0] + factors)
  
imports: import numpy
  from numpy.polynomial.legendre import legval
  from scipy.interpolate import RectBivariateSpline
  from scipy.linalg import pinv
  from scipy.spatial.distance import pdist, squareform
  from .._fiff.meas_info import _simplify_info
  from .._fiff.pick import pick_channels, pick_info, pick_types
  from ..surface import _normalize_vectors
  from ..utils import _validate_type, logger, verbose, warn
label_desc: Use image node_id 2 for calling a global function with example usage: _calc_g(cosang, stiffness, n_legendre_terms) and returns: legval