%設(shè)置全局變量
global meas species bad numobs
global  x y j tree


%Treefit函數(shù)能為數(shù)據(jù)集找到適合的決策樹(shù)。
%我們?yōu)檫@個(gè)Iris花數(shù)據(jù)集創(chuàng)建一棵決策樹(shù)
%并且觀察它在分類(lèi)Iris花的種群時(shí)候的好處和優(yōu)勢(shì)。

tree = treefit(meas(:,1:2), species);

% treeval計(jì)算決策樹(shù)的代價(jià)
[dtnum,dtnode,dtclass] = treeval(tree, meas(:,1:2));

%計(jì)算決策樹(shù)分類(lèi)誤差
bad_d = ~strcmp(dtclass,species);
sum(bad_d) / numobs

%創(chuàng)建含有x軸，y軸的柵格圖來(lái)顯示決策樹(shù)分類(lèi)區(qū)域
[grpnum,node,grpname] = treeval(tree, [x y]);
gscatter(x,y,grpname,'gmb','svp')
xlabel('萼片長(zhǎng)度');
ylabel('萼片寬度');
hold on;
plot(meas(bad_d,1), meas(bad_d,2), 'kx');
hold off;