Emgu CV: OpenCV in .NET (C#, VB, C++ and more)

I know that response is represented strength of keypoint, but i confused how is opencv compute the value of response,
anyone now the formula?
please help me, it is important to my graduation

Here is original SURF paper:
ftp://ftp.vision.ee.ethz.ch/publication ... _00517.pdf

and a Open CV SURF tutorial in python (the idea is the same):
http://docs.opencv.org/3.0-beta/doc/py_ ... intro.html

Hope this helps.