> The Spider Objects

>       DATA_GLOBAL object

>        Stores data into two components X (input) and Y (output).
>        The difference to the data object consists in storing data in global
>        variables X and Y to avoid them to be copied on new functions calls. This
>        reduces memory overheads.

>        An object is created with:
>          data_global('name',X,Y);
>              or
>          data_global(X,Y);
>              or
>          data_global(X) (in case there's no name)

>          If you want to create it with globals, define X and Y and call
>          data_global('name') or just data_global.

>        Public attributes:
>         X          -- input matrix
>         Y          -- output matrix
>         index      -- original parent indices of examples
>         findex     -- original parent indices of features

>        Public methods:
>         d=get(data,index,featInd)             -- return data,index only (ind)examples,(find)features
>         x=get_x(data,index,fInd)              -- return x,index only (ind)examples,(find)features
>         y=get_y(data,index,fInd)              -- return y,index only (ind)examples,(find)features
>         d=set_x(data,X,indes,featInd)         -- set inputs indexed by (ind)examples,(find)features
>         d=set_y(data,Y,index,featInd)         -- set outputs indxed by (ind)examples,(find)features
>         [indes,featInd]=get_index(d)          -- returns example and feature indices
>         [numEx,vDim,oDim,numCls]=get_dim(d)   -- returns number of examples,features,output dimensions,classes

>        Example:
>                 global X; X=[1:5;6:10;11:15]; get_x(data_global('gi'),[1 3],[3:5])

>        Note:
>        Fast storage of data is achieved by using global X, i.e  X(index,findex).
>        xx and yy (optionally) can be stored if different from original. If
>        xx is empty then it is assumed to be equal to global X with given indexes. The same is considered
>        for yy ALSO, even if xx instantiated, always global Y(index,:) is used.