Notes on Math

Logarithmic Functio
http://www.mathsisfun.com/sets/function-logarithmic.html
f(x) = loga(x)
loga(x)   is the Inverse Function of  ax (the Exponential Function)

The Natural Logarithm Function
f(x) = loge(x)
f(x) = ln(x)
Where e is "Eulers Number" = 2.718281828459 (and more ...)

confusion matrix
【计算机】干扰矩阵， 混淆矩阵
http://en.wikipedia.org/wiki/Confusion_matrix

http://www2.cs.uregina.ca/~dbd/cs831/notes/confusion_matrix/confusion_matrix.html

In the field of machine learning, a confusion matrix, also known as a contingency table or an error matrix [1] , is a specific table layout that allows visualization of the performance of an algorithm, typically a supervised learning one (in unsupervised learning it is usually called a matching matrix). 
The name stems from the fact that it makes it easy to see if the system is confusing two classes (i.e. commonly mislabeling one as another).

Predicted class
Cat	Dog	Rabbit
Actual class	Cat	5	3	0
	Dog	2	3	1
	Rabbit	0	2	11