anchor.diff:  during the learning or mean field is used instead. :HALF-HEARTED, the
   default value, samples the hiddens but uses the hidden means to
   calculate the effect of the positive and negative phases on the
  -gradient.")
  +gradient. The default should almost always be preferable to T, as it
  +is a less noisy estimate.")
      (n-gibbs
       :type (integer 1)
       :initform 1
       :initarg :n-gibbs
       :accessor n-gibbs
  -    :documentation "The number of steps of Gibbs sampling to perform."))
  +    :documentation "The number of steps of Gibbs sampling to perform.
  +This is how many full (HIDDEN -> VISIBLE -> HIDDEN) steps are taken
  +for CD learning, and how many times each chunk is sampled for PCD."))
     (:documentation "Paramaters for Markov Chain Monte Carlo based
   trainers for BMs."))
   
positive.code: 
  (defun hijack-means-to-activation (chunks clouds bm &key addp)
    "Set NODES of CHUNKS to the activations calculated from CLOUDS. Skip
  chunks that don't need activations."
    (destructuring-bind (static-activations-context static-chunks)
        (or (rest (find bm *static-activation-contexts* :key #'first))
            (list (gensym) nil))
  
negative.code: \(optionally) a sample is taken from the probability distribution. All
  these values are stored in this vector. This is also where SET-INPUT
  is supposed to clamp the values. Note that not only the values in the
  matrix but also the matrix object itself can change when the network
  is used.")
     (old-nodes
      :type matlisp:real-matrix :reader old-nodes
      :documentation "The previous value of each node. Used to provide
  parallel computation semantics when there are intralayer connections.
  Swapped with NODES or MEANS at times.")
     (means
      :type (or matlisp:real-matrix null) :reader means
      :documentation "Saved values of the means (see SET-MEAN) last
  computed.")
     (inputs
      :type (or matlisp:real-matrix null) :reader inputs
      :documentation "This is where the after method of SET-INPUT saves
  the input for later use by RECONSTRUCTION-ERROR, INPUTS->NODES. It is
  NIL in CONDITIONING-CHUNKS.")
     (cache-static-activations-p
      :initform nil
      :initarg :cache-static-activations-p
  