Well, it's not a typo, since you wrote it twice. Your 1st msg wa

来源: 于 2015-03-07 06:09:11 [博客] [旧帖] [给我悄悄话] 本文已被阅读：次

is "non negative definite".
Then you changed it to sinc(x), continue to call it "NND".
How cute. You want to show-off a little here but continue to get the basic concept wrong.

The third correction for you: F(sinc) is not "NND", it's just "NN"
Lol