prtKernelDirect  Direct kernel
 
   kernelObj = prtKernelDirect Generates a prtKernelDirect object implementing a
   direct kernel function.  Kernel objects are widely used in several
   prt classifiers, such as prtClassRvm and prtClassSvm.  Direct kernels
   implement the following function for 1 x N vectors x1 and x2:
 
    k(x1,x2) = x2;
 
   Direct kernel functions can be used sparse machine learning contexts
   to perform sparse linear feature selection.
    
   prtKernelDirect objects inherit the TRAIN, RUN, and AND
   methods from prtKernel.
 
   % Example:
    ds = prtDataGenUnimodal;   % Load a data set
    k1 = prtKernelDirect;      % Create a prtKernelDirect object
    
    k1 = k1.train(ds);         % Train
    g1 = k1.run(ds);           % Run
 
    % Plot the results
    imagesc(g1.getObservations);