This class partially implements the generic interface
  defined for general algorithms defined in the NMF
  package (see algorithmic-NMF).
is.mixed tells if an NMF algorithm works on
  mixed-sign data.
S4 (NMFStrategy) `show`(object) S4 (NMFStrategy) `objective`(object) S4 (NMFStrategy,character) `objective`(object) <- value S4 (NMFStrategy,function) `objective`(object) <- value is.mixed(object)
(x="NMF", y="matrix") and return a nonnegative
  real value.
  
      signature(x = "NMFStrategy", y =
  "character"): Tells if an NMF algorithm can fit a given
  class of NMF models
  
      signature(x = "NMFStrategy", y =
  "NMF"): Tells if an NMF algorithm can fit the same class
  of models as y
  
      signature(object = "NMFStrategy"):
  Computes the value of the objective function between the
  estimate x and the target y.
  
      signature(object =
  "NMFStrategy"): Returns the model(s) that an NMF
  algorithm can fit.
  
      signature(name = "NMFStrategy",
  method = "missing"): Creates an NMFStrategy based
  on a template object (Constructor-Copy), in particular it
  uses the same name.
  
      signature(object =
  "NMFStrategy"): Gets the objective function associated
  with an NMF algorithm.
  
      It is used in
  deviance to
  compute the objective value for an NMF model with respect
  to a given target matrix.
signature(object =
  "NMFStrategy"): Gets the objective function associated
  with an NMF algorithm.
  
      It is used in
  deviance to
  compute the objective value for an NMF model with respect
  to a given target matrix.
signature(object =
  "NMFStrategy", value = "character"): Sets the objective
  function associated with an NMF algorithm, with a
  character string that must be a registered objective
  function.
  
      signature(object =
  "NMFStrategy", value = "character"): Sets the objective
  function associated with an NMF algorithm, with a
  character string that must be a registered objective
  function.
  
      signature(object =
  "NMFStrategy", value = "function"): Sets the objective
  function associated with an NMF algorithm, with a
  function that computes the approximation error between an
  NMF model and a target matrix.
  
      signature(object =
  "NMFStrategy", value = "function"): Sets the objective
  function associated with an NMF algorithm, with a
  function that computes the approximation error between an
  NMF model and a target matrix.
  
      signature(object = "NMFStrategy", y =
  "matrix", x = "NMFfit"): Pure virtual method defined for
  all NMF algorithms to ensure that a method run is
  defined by sub-classes of NMFStrategy.
  
      It throws an error if called directly.
signature(object = "NMFStrategy", y =
  "matrix", x = "NMF"): Method to run an NMF algorithm
  directly starting from a given NMF model.