function?[auc?curve]?=?ROC（score?target?Lp?Ln）

%?	This?function?is?to?calculat?the?ordinats?of?points?of?ROC?curve?and?the?area
%?under?ROC?curve（AUC）.
%????This?program?was?described?in?Fawcett‘s?paper?“ROC?Graphs:?notes?and?practical
%?considerations?for?researchers“.
%?
%?Output:
%????curve:?N*3?matrix.?
%????????????the?1st?column?is?FP?
%????????????the?2nd?column?is?TP
%????????????the?3rd?column?is?score
%????????????note:?the?last?row?etc.the?last?point?is?[110].?if?output?of?this
%???????????????function?is?applied?to?roc_av.m?to?calculate?average?curve?of?roc?
%???????????????it?should?be?delete
%????auc:???scale?number?area?under?ROC?curve.
%?
%?Input?parameters:
%????score:??output?of?classifier.?high?socre?denote?the?pattern?is?more?likely?
%????????????to?be?POSITIVE?pattern.
%????target:?classlabel?of?each?pattern.
%????Lp:?????label?of?POSITIVE?pattern.??
%????Ln:?????label?of?NEGATIVE?pattern.
%?
%
%?QingRen??（qingren_ny#126.com）
%?2006-7-20
%?
?????????

len?=?length（score）;????????????????%?number?of?patterns
if?len?~=?length（target）
	error（‘The?length?of?tow?input?vectors?should?be?equal\n‘）;
end

P?=?0;????%?number?of?Positive?pattern
N?=?0;????%?number?of?Negative?pattern
for?i?=?1:len
	if?target（i）?==?Lp
		P?=?P?+?1;
	elseif?target（i）?==?Ln
		N?=?N?+?1;
	else
		error（‘Wrong?target?value‘）;
	end
end



%?sort?“L“??in?decending?order?by?scores
score?=?score（:）;
target?=?target（:）;
L?=?[score?target];
L?=?sortrows（L1）;
index?=?len:-1:1;
index?=?index‘;?????%‘
L?=?L（index:）;



fp?=?0;???fp_pre?=?0;???%?number?of?False?Positive?pattern
tp?=?0;???tp_pre?=?0;???%?number?of?True?Positive?pattern.

score_pre?=?-10000;

curve?=?[];
auc?=?0;

for?i?=?1:len
	if?L（i1）?~=?score_pre
		curve?=?[curve;?[fp/N?tp/P?L（i1）]];
		auc?=?auc?+?trapezoid（fp?fp_pre?tp?tp_pre）;
		
		score_pre?=?L（i1）;
		
		fp_pre?=?fp;
		tp_pre?=?tp;
	end
	
	if?L（i2）?==?Lp
		tp?=?tp?+?1;
	else
		fp?=?fp?+?1;
	end
end

curve?=?[curve;?[110]];

auc?=?auc?/?P?/?N;
auc?=?auc?+?trapezoid（1?fp_pre/N?1?tp_pre/P）;





%?calculat?the?area?of?trapezoid

function?area?=?trapezoid（x1x2y1y2）
a?=?abs（x1-x2）;
b?=?abs（y1+y2）;
area?=?a?*?b?/?2;

?屬性????????????大小?????日期????時間???名稱
-----------?---------??----------?-----??----

?????文件???????2276??2006-12-24?10:25??roc.m

-----------?---------??----------?-----??----

?????????????????2276????????????????????1