class_docstr: Results class for generalized additive models, GAM.
  
  This inherits from GLMResults.
  
  Warning: some inherited methods might not correctly take account of the
  penalization
  
  GLMGamResults inherits from GLMResults
  All methods related to the loglikelihood function return the penalized
  values.
  
  Attributes
  ----------
  
  edf
      list of effective degrees of freedom for each column of the design
      matrix.
  hat_matrix_diag
      diagonal of hat matrix
  gcv
      generalized cross-validation criterion computed as
      ``gcv = scale / (1. - hat_matrix_trace / self.nobs)**2``
  cv
      cross-validation criterion computed as
      ``cv = ((resid_pearson / (1 - hat_matrix_diag))**2).sum() / nobs``
  
  Notes
  -----
  status: experimental
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code: def cv(self):
      cv_ = (
          (self.resid_pearson / (1.0 - self.hat_matrix_diag)) ** 2
      ).sum()
      cv_ /= self.nobs
      return cv_
  
imports: from collections.abc import Iterable
  import copy
  import numpy
  from scipy import optimize
  import pandas
  import statsmodels.base.wrapper
  from statsmodels.discrete.discrete_model import Logit
  from statsmodels.genmod.generalized_linear_model import GLM, GLMResults, GLMResultsWrapper, _check_convergence
  import statsmodels.regression.linear_model
  from statsmodels.tools.sm_exceptions import PerfectSeparationError, ValueWarning
  from statsmodels.tools.decorators import cache_readonly
  from statsmodels.tools.data import _is_using_pandas
  from statsmodels.tools.linalg import matrix_sqrt
  from statsmodels.base._penalized import PenalizedMixin
  from statsmodels.gam.gam_penalties import MultivariateGamPenalty
  from statsmodels.gam.gam_cross_validation.gam_cross_validation import MultivariateGAMCVPath
  from statsmodels.gam.gam_cross_validation.cross_validators import KFold
label_desc: Use image node_id 13 for calling the GLMGamResults obj's underlying member method code with example usage: obj.cv() and returns: cv_