> The Spider Objects

>       RSC_MDS reduced set construction - using MDS

>        a = rsc_mds(alg,hyper)
>        generates a rsc object, using the MDS pre-images method

>        hyperparameters:
>        child=svm     algorithm worked on
>        rsv=.5        if rsv e [0,1): #rsv = #sv * rsv
>                      if rsv > 1: #rsv
>        nn=10         neighbours to use for distance constraints
>        map='rbf_map' supply function name to be called for calculating
>                      input space distances from feature space distances
>                      must be supplied in rsc_mds directory

>        model:
>        alpha         new alphas for rs-vectors
>        Xsv           rs vectors

>        stats:
>        w2=0          final value of ||w-w*||^2
>        delta_w=0     total decrease in ||w-w*||^2
>        dw=0          run through delta_w

>        methods:
>        train         constructs a reduced set, returns trained rs-machine
>        test          tests new rs-machine on supplied data

>        example:
>        d=gen(toy2d('2circles','l=100'));
>        [r,a]=train(svm({kernel('rbf',1),'C=10000','alpha_cutoff=1e-2'}),d);
>        [r,a2]=train(rsc_mds(a,'rsv=.9'),d);
>        test(a2,d,loss)

>        remark: supports only rbf kernels up per default!

>        author: Goekhan BakIr, Philipp Berens
>        reference: The Pre-Image Problem in Kernel Methods, J.T.Kwok, 2004