docstr: Mean diffusivity.
  
  Returns
  -------
  md : numpy.ndarray
  
  Notes
  -----
  Mean diffusivity is calculated as
  
      .. math::
  
                  ext{MD} = \langle \mathbf{D} 
  angle : \mathbf{E}_     ext{iso}
docstr_tok: ["Mean","diffusivity",".","Returns","--","--","--","-","md",":","numpy.ndarray","Notes","--","--","-","Mean","diffusivity","is","calculated","as","..","math",":",":","ext","{","MD","}","=","\\langle","\\mathbf","{","D","}","angle",":","\\mathbf","{","E","}","_","ext","{","iso","}"]
code: def md(self):
      """Mean diffusivity.
  
      Returns
      -------
      md : numpy.ndarray
  
      Notes
      -----
      Mean diffusivity is calculated as
  
          .. math::
  
              \text{MD} = \langle \mathbf{D} \rangle : \mathbf{E}_\text{iso}
      """
      md = np.matmul(
          self.params[..., np.newaxis, 1:7], from_3x3_to_6x1(e_iso)
      )[..., 0, 0]
      return 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 4 for calling the QtiFit obj's underlying member method code with example usage: obj.md() and returns: md