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曲线面积的求法:
(1)任意曲线的面积求法:
>> x=0:pi/100:pi; >> y=sin(x); >> trapz(x,y) ans = 1.9998
(2)ROC曲线的面积求法:function auc=auc(FPR,TPR) % given true positive rate and false positive rate calculates the area under the curve % true positive are on the y-axis and false positives on the x-axis % sum rectangular area between all points % example: auc=auc(FPR,TPR); [x2,inds]=sort(FPR); x2=[x2,1]; % the trick is in inventing a last point 1,1 y2=TPR(inds); y2=[y2,1]; xdiff=diff(x2); %xdiff xdiff=[x2(1),xdiff]; auc1=sum(y2.*xdiff); % upper point area auc2=sum([0,y2([1:end-1])].*xdiff); % lower point area auc=mean([auc1,auc2]); end