docstr: Variance of microscopic mean diffusivities.
  
  Returns
  -------
  v_md : numpy.ndarray
  
  Notes
  -----
  Variance of microscopic mean diffusivities is calculated as
  
      .. math::
  
          V_      ext{MD} = \mathbb{C} : \mathbb{E}_      ext{bulk}
docstr_tok: ["Variance","of","microscopic","mean","diffusivities",".","Returns","--","--","--","-","v_md",":","numpy.ndarray","Notes","--","--","-","Variance","of","microscopic","mean","diffusivities","is","calculated","as","..","math",":",":","V_","ext","{","MD","}","=","\\mathbb","{","C","}",":","\\mathbb","{","E","}","_","ext","{","bulk","}"]
code: def v_md(self):
      """Variance of microscopic mean diffusivities.
  
      Returns
      -------
      v_md : numpy.ndarray
  
      Notes
      -----
      Variance of microscopic mean diffusivities is calculated as
  
          .. math::
  
              V_\text{MD} = \mathbb{C} : \mathbb{E}_\text{bulk}
      """
      v_md = np.matmul(
          self.params[..., np.newaxis, 7::], from_6x6_to_21x1(E_bulk)
      )[..., 0, 0]
      return v_md
  
imports: from warnings import warn
  import numpy
  from dipy.reconst.base import ReconstModel
  from dipy.reconst.dti import auto_attr
  from dipy.utils.optpkg import optional_package
label_desc: Use image node_id 5 for calling the QtiFit obj's underlying member method code with example usage: obj.v_md() and returns: v_md