下面SAS语言在执行什么命令，看不懂，求解释，谢谢！

ods graphics on;

proc logistic data=tmpp1 desc plots(only)=roc;

model y(event='1')=x1 x2 x3 你的校正变量/nofit;

roc 'X1' x1;

roc 'X2' x2;

roc 'X3' x3;

roccontrast reference('X1') / estimate e;*/

run;

ods graphics off;