class_docstr: Cox proportional hazards model.
  
  There are two possible choices for handling tied event times.
  The default is Breslow's method, which considers each of the
  events at a given time as distinct. Efron's method is more
  accurate if there are a large number of ties. When the number
  of ties is small, the estimated coefficients by Breslow's and
  Efron's method are quite close. Uses Newton-Raphson optimization.
  
  See [1]_, [2]_, [3]_ for further description.
  
  Parameters
  ----------
  alpha : float, ndarray of shape (n_features,), optional, default: 0
      Regularization parameter for ridge regression penalty.
      If a single float, the same penalty is used for all features.
      If an array, there must be one penalty for each feature.
      If you want to include a subset of features without penalization,
      set the corresponding entries to 0.
  
  ties : {'breslow', 'efron'}, optional, default: 'breslow'
      The method to handle tied event times. If there are
      no tied event times all the methods are equivalent.
  
  n_iter : int, optional, default: 100
      Maximum number of iterations.
  
  tol : float, optional, default: 1e-9
      Convergence criteria. Convergence is based on the negative log-likelihood::
  
      |1 - (new neg. log-likelihood / old neg. log-likelihood) | < tol
  
  verbose : int, optional, default: 0
      Specifies the amount of additional debug information
      during optimization.
  
  Attributes
  ----------
  coef_ : ndarray, shape = (n_features,)
      Coefficients of the model
  
  cum_baseline_hazard_ : :class:`sksurv.functions.StepFunction`
      Estimated baseline cumulative hazard function.
  
  baseline_survival_ : :class:`sksurv.functions.StepFunction`
      Estimated baseline survival function.
  
  n_features_in_ : int
      Number of features seen during ``fit``.
  
  feature_names_in_ : ndarray of shape (`n_features_in_`,)
      Names of features seen during ``fit``. Defined only when `X`
      has feature names that are all strings.
  
  unique_times_ : array of shape = (n_unique_times,)
      Unique time points.
  
  See also
  --------
  sksurv.linear_model.CoxnetSurvivalAnalysis
      Cox proportional hazards model with l1 (LASSO) and l2 (ridge) penalty.
  
  References
  ----------
  .. [1] Cox, D. R. Regression models and life tables (with discussion).
         Journal of the Royal Statistical Society. Series B, 34, 187-220, 1972.
  .. [2] Breslow, N. E. Covariance Analysis of Censored Survival Data.
         Biometrics 30 (1974): 89–99.
  .. [3] Efron, B. The Efficiency of Cox’s Likelihood Function for Censored Data.
         Journal of the American Statistical Association 72 (1977): 557–565.
code: def cum_baseline_hazard_(self):
      return self._baseline_model.cum_baseline_hazard_
  
imports: import numbers
  import warnings
  import numpy
  from scipy.linalg import solve
  from sklearn.base import BaseEstimator
  from sklearn.exceptions import ConvergenceWarning
  from sklearn.utils._param_validation import Interval, StrOptions
  from sklearn.utils.validation import check_array, check_is_fitted
  from ..base import SurvivalAnalysisMixin
  from ..functions import StepFunction
  from ..nonparametric import _compute_counts
  from ..util import check_array_survival
label_desc: Use image node_id 2 for calling the CoxPHSurvivalAnalysis obj's underlying member method code with example usage: obj.cum_baseline_hazard_() and returns: self