class_docstr: Cosine transformation.
  
  This is a wrapper around numpy's cosine function (see :func:`numpy.cos`).
  
  See Also
  --------
  numpy.cos
  
  Examples
  --------
  >>> from sktime.transformations.series.cos import CosineTransformer
  >>> from sktime.datasets import load_airline
  >>> y = load_airline()
  >>> transformer = CosineTransformer()
  >>> y_hat = transformer.fit_transform(y)
docstr: Transform X and return a transformed version.
  
  private _transform containing the core logic, called from transform
  
  Parameters
  ----------
  X : 2D np.ndarray
      Data to be transformed
  y : ignored argument for interface compatibility
      Additional data, e.g., labels for transformation
  
  Returns
  -------
  Xt : 2D np.ndarray
      transformed version of X
docstr_tok: ["Transform","X","and","return","a","transformed","version",".","private","_transform","containing","the","core","logic",",","called","from","transform","Parameters","--","--","--","--","--","X",":","2D","np.ndarray","Data","to","be","transformed","y",":","ignored","argument","for","interface","compatibility","Additional","data",",","e.g.",",","labels","for","transformation","Returns","--","--","--","-","Xt",":","2D","np.ndarray","transformed","version","of","X"]
code: def _transform(self, X, y=None):
      """Transform X and return a transformed version.
  
      private _transform containing the core logic, called from transform
  
      Parameters
      ----------
      X : 2D np.ndarray
          Data to be transformed
      y : ignored argument for interface compatibility
          Additional data, e.g., labels for transformation
  
      Returns
      -------
      Xt : 2D np.ndarray
          transformed version of X
      """
      Xt = np.cos(X)
      return Xt
  
imports: from math import pi
  import numpy
  from sktime.transformations.base import BaseTransformer
label_desc: Use image node_id 1 for calling the CosineTransformer obj's underlying member method code with example usage: obj._transform(X, y) and returns: Xt