shows the two-class classification boundary of the 2-D data
libsvm_toy(label_vector, instance_matrix, options, contour_level)
N by 1, has to be two-class
N by 2
default '', see svmtrain, has to be a classification formulation (e.g."-c 1000 -g 0.5") .
default [0 0], change to [-1 0 1] for showing the +/- 1 margin.
libsvm_toy shows the two-class classification boundary of the 2-D data