ndi.fun.calc.stimulus_tuningcurve_log

  STIMULUS_TUNINGCURVE_LOG - retrieve stimulus_tuningcurve log string from dependent document

  LOG_STR = STIMULUS_TUNINGCURVE_LOG(S, DOC)

  Given an ndi.document that has a dependency 'stimulus_tuningcurve_id'
  that was created by ndi.calc.stimulus.tuningcuve, 
  this function looks up the DOC's dependent tuningcurve_calc document
  and retrieves the 'log' string field.