Why do you typically see overflow and underflow when implementing an ML algorithms ?

A common pre-processing step is to normalize/rescale inputs so that they are not too high or low. However, even on normalized inputs, overflows and underflows can occur: Underflow: Joint probability distribution often involves multiplying small individual probabilities. Many probabilistic algorithms involve multiplying probabilities of individual data points that leads to underflow. Example : Suppose you…

With the maximum likelihood estimate are we guaranteed to find a global Optima ?

Maximum likelihood estimate finds that value of parameters that maximize the likelihood. If the likelihood is strictly concave(or negative of likelihood is strictly convex), we are guaranteed to find a unique optimum. This is usually not the case and we end up finding a local optima. Hence, the Maximum likelihood estimate usually finds a local…

What are evaluation metrics for multi-class classification problem (like positive/negative/neutral sentiment analysis)

For multiclass classification(MCC) problems, metrics  can be derived from the confusion matrix. Let $tp_i,tn_i,fp_i,fn_i$ denote the true positives, true negatives, false positives, false negatives respectively. MCC problems, usually macro and micro metrics are computed: → Micro metrics (with subscript $\mu$ in table below) are computed by summing up individual tp, tn, fp and fn to…

What is page rank algorithm ?

Quote from wikipedia: A PageRank results from a mathematical algorithm based on the webgraph, created by all World Wide Web pages as nodes and hyperlinks as edges, taking into consideration authority hubs such as cnn.com or usa.gov. The rank value indicates an importance of a particular page. A hyperlink to a page counts as a…

You want to find food related topics in twitter – how do you go about it ?

One can use any of the topic models above to get topics. However, to direct the topics to contain food related information, specialized topic modeling algorithms are available. However, one simple way to direct the topics to food related things is : Filter tweets by a limited set of food related keywords (food, meal, dinner,…