A. Bhattacharya
Encyclopedia
A. Bhattacharya was an Indian statistician
Statistician
A statistician is someone who works with theoretical or applied statistics. The profession exists in both the private and public sectors. The core of that work is to measure, interpret, and describe the world and human activity patterns within it...

 who worked at the Indian Statistical Institute
Indian Statistical Institute
Indian Statistical Institute is a public research institute and university in Kolkata's northern outskirt of Baranagar, India founded by Prasanta Chandra Mahalanobis in 1931...

 founded by P C Mahalanobis in the 1930s and early 40s. He made fundamental contributions to multivariate statistics
Multivariate statistics
Multivariate statistics is a form of statistics encompassing the simultaneous observation and analysis of more than one statistical variable. The application of multivariate statistics is multivariate analysis...

, particularly for his measure of similarity between two multinomial distributions, known as the Bhattacharya coefficient, based on which he defined a metric
Metric (mathematics)
In mathematics, a metric or distance function is a function which defines a distance between elements of a set. A set with a metric is called a metric space. A metric induces a topology on a set but not all topologies can be generated by a metric...

, the Bhattacharya distance. This measure is widely used in comparing statistical samples in biology, physics, computer science, etc. His surname (Bangla: ভট্টাচার্য) used to be spelled Bhattacharyya earlier.

Distance between statistical distributions had been addressed in 1936 by Bhattacharyya's mentor, Mahalanobis, who proposed the D2 metric, now known as Mahalanobis distance
Mahalanobis distance
In statistics, Mahalanobis distance is a distance measure introduced by P. C. Mahalanobis in 1936. It is based on correlations between variables by which different patterns can be identified and analyzed. It gauges similarity of an unknown sample set to a known one. It differs from Euclidean...

. Subsequently Bhattacharya defined a cosine metric
Cosine similarity
Cosine similarity is a measure of similarity between two vectors by measuring the cosine of the angle between them. The cosine of 0 is 1, and less than 1 for any other angle. The cosine of the angle between two vectors thus determines whether two vectors are pointing in roughly the same...

 for distance between distributions, in a Calcutta Mathematical Society
Calcutta Mathematical Society
The Calcutta Mathematical Society is an association of professional mathematicians dedicated to the interests of mathematical research and education in India...

paper in 1943, expanding on some of the results in another paper in Sankhya in 1947.

Sometime in the 1940s, Bhattacharya left ISI to join a government job, most likely at a rural college teaching mathematics. He did not publish thereafter.
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