%設置全局變量
global meas species bad numobs
global  x y j tree


%Treefit函數能為數據集找到適合的決策樹。
%我們為這個Iris花數據集創建一棵決策樹
%并且觀察它在分類Iris花的種群時候的好處和優勢。

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

% treeval計算決策樹的代價
[dtnum,dtnode,dtclass] = treeval(tree, meas(:,1:2));

%計算決策樹分類誤差
bad_d = ~strcmp(dtclass,species);
sum(bad_d) / numobs

%創建含有x軸，y軸的柵格圖來顯示決策樹分類區域
[grpnum,node,grpname] = treeval(tree, [x y]);
gscatter(x,y,grpname,'grb','sop')
xlabel('萼片長度');
ylabel('萼片寬度');
hold on;
plot(meas(bad_d,1), meas(bad_d,2), 'kx');
hold off;