Indian statistician (1936–2023)
Kalyanapuram Rangachari Parthasarathy (25 June 1936 – 14 June 2023) was an Indian statistician who was professor emeritus at the Indian Statistical Institute and a pioneer of quantum stochastic calculus. Parthasarathy was the recipient of the Shanti Swarup Bhatnagar Prize for Science and Technology in Mathematical Science in 1977 and the TWAS Prize in 1996.
Biography.
Parthasarathy was born on 25 June 1936 in Madras, into a modest but deeply religious Hindu Brahmin family. He completed his early years of schooling in Thanjavur, before moving back to Madras to complete his schooling from P. S. School in the Mylapore neighbourhood of the city. He went on to study at the Ramakrishna Mission Vivekananda College, where he completed the B.A. (Honours) course in Mathematics. 
Parthasarathy then moved to Kolkata to attend the Research and Training school at the Indian Statistical Institute, where he completed his Ph.D., under the supervision of C. R. Rao in 1962. He was one of the "famous four" at ISI from 1956 to 1963, alongside R. Ranga Rao, Veeravalli S. Varadarajan, and S. R. Srinivasa Varadhan. He was awarded the first Ph.D. degree of ISI. 
He received the Shanti Swarup Bhatnagar Prize for Science and Technology in Mathematical Science in 1977 and The World Academy of Sciences (TWAS) Prize for Mathematics in 1996.
Parthasarathy was married to Shyama Parthasarathy. The couple had two sons. Parthasarathy died in Delhi on 14 June 2023, at the age of 86.
Research.
Parthasarathy started his work on theoretical probability during his time at the Indian Statistical Institute. He later worked at the Steklov Mathematical Institute, USSR Academy of Sciences (1962–63), as lecturer where he collaborated with Andrey Kolmogorov. During this time, he continued to focus on the foundations of probability theory. Later he came to the United Kingdom as a Professor of Statistics at University of Sheffield (1964–68), University of Manchester (1968–70) and later at University of Nottingham where he collaborated with Robin Lyth Hudson on their pioneering work in quantum stochastic calculus. 
After returning to India, he spent a few years at Bombay University and the Indian Institute of Technology, Delhi, before returning to the new Indian Statistical Institute, Delhi Centre, in 1976, where he spent the next 20 years before retiring in 1996. He continued to remain as a professor emeritus at the institute until the early 2020s.
Parthasarathy is the namesake of Kostant–Parthasarathy–Ranga Rao–Varadarajan determinants along with Bertram Kostant, R. Ranga Rao and Veeravalli S. Varadarajan which they introduced in 1967. He collaborated with Ranga Rao and Varadarajan to write a paper on representation theory of lie groups referred to as the PRV paper that was the foundation for further research on this topic.
In addition to pioneering contributions to quantum stochastic calculus, some of Parthasarathy's research areas included quantum probability, foundations of quantum mechanics, information theory, stochastic processes, and group representations. He also served on many governmental committees.
References.
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