HW 4.1: fig1.m.
HW 4.2: fig2.m, rbfweight.m, rbfbndline.m, rbf.m.
HW 4.3: fig3.m, kneighbor.m, kneighest.m.
HW 4.4: rbf2.m, cluster.m, rbf2weight.m.
Subroutines: plotdata.m, dist2.m.