docs: def quattodcm(quat):
      """Convert quaternion to DCM
  
      This function will convert a quaternion to the equivalent rotation matrix,
      or direction cosine matrix.
  
      Parameters:
      ----------
      quat - (4,) numpy array
          Array defining a quaterion where the quaternion is defined in terms of
          a vector and a scalar part.  The vector is related to the eigen axis
          and equivalent in both reference frames [x y z w]
  
      Returns:
      --------
      dcm - (3,3) numpy array
          Numpy rotation matrix which defines a rotation from the b to a frame
      """
  
      dcm = (quat[-1]**2-np.inner(quat[0:3], quat[0:3]))*np.eye(3,3) + 2*np.outer(quat[0:3],quat[0:3]) + 2*quat[-1]*hat_map(quat[0:3])
  
      return dcm