size 10 8 include "color.gle" set font texcmr tpos = 50; tneg = 50 tot = tpos + tneg sub entropy p if (p = 0) or (p = 1) then return 0 else return -p*log(p)/log(2) - (1-p)*log(1-p)/log(2) end sub sub information_gain lpos lneg local rpos = tpos - lpos local rneg = tneg - lneg local ltot = lpos + lneg local rtot = rpos + rneg return entropy(tpos/tot) - & ltot/tot*entropy(sdiv(lpos,ltot)) - rtot/tot*entropy(sdiv(rpos,rtot)) end sub begin graph xaxis min 0 max tpos yaxis min 0 max tneg title "Information Gain" xtitle "# positives in left branch" ytitle "# negatives in left branch" colormap information_gain(x,y) 250 250 color end graph set hei 0.29 amove xg(xgmax)+0.3 yg(ygmin) color_range_vertical zmin 0 zmax 1 zstep 0.1 pixels 500 format "fix 1"