code: def rotation_mat2vec(R):
      """Rotation vector from rotation matrix `R`
  
      Parameters
      ----------
      R : (3,3) array-like
          Rotation matrix
  
      Returns
      -------
      vec : (3,) array
          Rotation vector, where norm of `vec` is the angle ``theta``, and the
          axis of rotation is given by ``vec / theta``
      """
      ax, angle = quat2axangle(mat2quat(R))
      return ax * angle
  
imports: import numpy
  import scipy.linalg
  from nibabel.affines import apply_affine
  from transforms3d.quaternions import mat2quat, quat2axangle
  from .transform import Transform
label_desc: Use image node_id 2 for calling a global function with example usage: rotation_mat2vec(R) and returns: unknown