code: def vec(M):
      """
      Stack columns of M to construct a single vector.
  
      This is somewhat standard notation in linear algebra.
  
      Parameters
      ----------
      M : 2d array_like
          Input matrix
  
      Returns
      -------
      v : 1d ndarray
          Output vector
  
      """
      return M.T.ravel()
  
file_path: catboost/contrib/python/scipy/py2/scipy/linalg/_expm_frechet.py
imports: from __future__ import division, print_function, absolute_import
  import numpy
  import scipy.linalg
label_desc: Use image node_id 8 for calling a global function with example usage: vec(M) and returns: M