> The Spider Objects

>            CLUSTUB object

>        A=CLUSTUB(H) returns a clustub object initialized with hyperparameters H.

>         Peforms feature selection via spectral clustering.

>        Hyperparameters, and their defaults
>         feat=[]              -- number of features
>         output_rank=0        -- set to 1 if only the feature ranking matters
>                                 (does not perform any classification on the data)
>         child=spectral('k=2')-- Clustering method used for training

>        Model
>         w                    -- the weights
>         b0                   -- the threshold (when using all features)
>         rank                 -- the ranking of the features
>         d                    -- training set

>        Methods:
>         train, test, get_w

>        Example:
>         d=gen(bayes({gauss([-1 3]) gauss([0 4]) gauss([1 2])}))
>         a=chain({clustub('output_rank=1'),one_vs_rest(svm('ridge=0.01'))})
>         [r,a]=train(a,d)

>        Note:
>         Method for multi-class feature selection.
>         To use with SVM, use:
>         chain({clustub('output_rank=1'),one_vs_rest(svm)})