entropy

问题 How to calculate the entropy of a file? (Or let\'s just say a bunch of bytes) I have an idea, but I\'m not sure that it\'s mathematically correct. My idea is the following: Create an array of 256 integers (all zeros). Traverse through the file and for each of its bytes, increment the corresponding position in the array. At the end: Calculate the \"average\" value for the array. Initialize a counter with zero, and for each of the array\'s entries: add the entry\'s difference to \"average\" to

问题 I have two black and white images and I need to calculate the mutual information. Image 1 = X Image 2 = Y I know that the mutual information can be defined as: MI = entropy(X) + entropy(Y) - JointEntropy(X,Y) MATLAB already has built-in functions to calculate the entropy but not to calculate the joint entropy. I guess the true question is: How do I calculate the joint entropy of two images? Here is an example of the images I\'d like to find the joint entropy of: X = 0 0 0 0 0 0 0 0 1 1 0 0 0

问题 If you want a cryptographically strong random numbers in Java, you use SecureRandom . Unfortunately, SecureRandom can be very slow. If it uses /dev/random on Linux, it can block waiting for sufficient entropy to build up. How do you avoid the performance penalty? Has anyone used Uncommon Maths as a solution to this problem? Can anybody confirm that this performance problem has been solved in JDK 6? 回答1: If you want true random data, then unfortunately you have to wait for it. This includes