docstr: Fractional anisotropy.
  
  Returns
  -------
  fa : numpy.ndarray
  
  Notes
  -----
  Fractional anisotropy is calculated as
  
      .. math::
  
                  ext{FA} = \sqrt{C_      ext{M}}
docstr_tok: ["Fractional","anisotropy",".","Returns","--","--","--","-","fa",":","numpy.ndarray","Notes","--","--","-","Fractional","anisotropy","is","calculated","as","..","math",":",":","ext","{","FA","}","=","\\sqrt","{","C_","ext","{","M","}","}"]
code: def fa(self):
      """Fractional anisotropy.
  
      Returns
      -------
      fa : numpy.ndarray
  
      Notes
      -----
      Fractional anisotropy is calculated as
  
          .. math::
  
              \text{FA} = \sqrt{C_\text{M}}
      """
      fa = np.sqrt(self.c_m)
      return fa
  
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 14 for calling the QtiFit obj's underlying member method code with example usage: obj.fa() and returns: fa