entropy

Okay, I guess this is entirely subjective and whatnot, but I was thinking about entropy sources for random number generators. It goes that most generators are seeded with the current time, correct? Well, I was curious as to what other sources could be used to generate perfectly valid, random (The loose definition) numbers. Would using multiple sources (Such as time + current HDD seek time [We're being fantastical here]) together create a "more random" number than a single source? What are the logical limits of the amount of sources? How much is really enough? Is the time chosen simply because

Is there a standard way to do this? Googling -- "approximate entropy" bits -- uncovers multiple academic papers but I'd like to just find a chunk of pseudocode defining the approximate entropy for a given bit string of arbitrary length. (In case this is easier said than done and it depends on the application, my application involves 16,320 bits of encrypted data (cyphertext). But encrypted as a puzzle and not meant to be impossible to crack. I thought I'd first check the entropy but couldn't easily find a good definition of such. So it seemed like a question that ought to be on StackOverflow!

In my project I need to compute the entropy of 0-1 vectors many times. Here's my code: def entropy(labels): """ Computes entropy of 0-1 vector. """ n_labels = len(labels) if n_labels <= 1: return 0 counts = np.bincount(labels) probs = counts[np.nonzero(counts)] / n_labels n_classes = len(probs) if n_classes <= 1: return 0 return - np.sum(probs * np.log(probs)) / np.log(n_classes) Is there a faster way? @Sanjeet Gupta answer is good but could be condensed. This question is specifically asking about the "Fastest" way but I only see times on one answer so I'll post a comparison of using scipy and

I am using this line to generate a sha1 id for node.js: crypto.createHash('sha1').digest('hex'); The problem is that it's returning the same id every time. Is it possible to have it generate a random id each time so I can use it as a database document id? Gabi Purcaru Have a look here: How do I use node.js Crypto to create a HMAC-SHA1 hash? I'd create a hash of the current timestamp + a random number to ensure hash uniqueness: var current_date = (new Date()).valueOf().toString(); var random = Math.random().toString(); crypto.createHash('sha1').update(current_date + random).digest('hex');

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 the counter. Well, now I'm stuck. How to "project" the counter result in such a way that all results would lie

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 0 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 Y = 0 0 0 0 0 0 0 0 0.38 0.82 0.38 0.04 0 0 0.32 0.82 0.68 0.17 0 0 0