Remembering PPD
(1936-2025)
November 3, 2025 | Sitabhra Sinha
Occasionally, individuals appear who leave a deep impression on the members of an academic institution without ever having any formal association with it. IMSc has been particularly lucky in having a number of such visitors, especially during the years when Balu led the institution. Several of them had been invited as guest faculty at the Chennai Mathematics Institute (CMI), which was yet to shift to its own premises. Balu had graciously arranged for their accommodation at IMSc Guest House, as a result of which we got the benefit of stalwarts such as Prof HS Mani being present on our campus over extended periods.
However, of all of them, the one who probably had the deepest influence on my thinking and also became a close personal friend was Puthan Purayil Divakaran, who insisted that all his friends (who could range from ages 9 to 90) call him PPD. I have often read about personalities who are ‘larger than life’ – PPD was among the very few people I have seen for whom this description fit like a glove. You could feel his immense joie de vivre even from the way he would stride across the campus on his way from the academic block to the guest house for joining the evening tea “ritual” that a small group of the physics faculty members (which included Rahul Basu, Ghanashyam Date and Gautam Menon, to mention a few of the regular members) would indulge in at 5:30 pm.
The topics in this evening “small talk” would range from bemoaning the fate of undergraduates who would want to discuss string theory but could not solve simple problems involving Newton’s laws of motion, to discussing a book that has just been profiled in the New York Review of Books. PPD was easily one of the most eloquent voices – his range of knowledge spanning mathematical physics (his area of specialization) to Indian temple design, a passion which I learnt later he had shared with his art historian wife, Odile, and whom he accompanied on research visits to medieval-era South Asian art sites.
I had little overlap with PPD academically. He had been a high-energy physicist at TIFR Bombay, from where he had retired in 1996. However, given his breadth of interests and gregarious nature, we soon found ourselves discussing various scientific topics, especially when he began to deliver a course of lectures on the history of mathematics at CMI. This was also the time when, by a curious set of coincidences, IMSc became a center of research on deciphering the inscriptions found at various sites of the Indus civilization. At the time, PPD and I had begun to attend the monthly lectures organized by our neighbouring institute, the Roja Muthiah Research Library (RMRL), which housed the Indus Research Center. It was set up as a repository of the archives of Iravatham Mahadevan and to also carry forward his pioneering work on epigraphy.
It turned out that PPD knew Mahadevan quite well, as the latter had been at TIFR in the late 1970s, where he had prepared his famous concordance of Indus inscriptions (which is now publicly available online through the RMRL curated site https://indusscript.in/). Helped by PPD’s introduction, Mahadevan was soon convinced (despite his initial protestations about “What can I say that mathematicians may want to hear”) to give a public talk at IMSc. It coincided with a visit by Mayank Vahia from TIFR Bombay, an astronomer who had become interested in ancient artifacts recording astronomical events (an area known as archaeo-astronomy). This made him interested in the figures inscribed on the Indus seals, and we soon had a small but enthusiastic band at the Institute discussing various aspects of the Indus civilization.
PPD was at this time already studying the origins of mathematics in the subcontinent. He was going through the Sulbasutras, the earliest mathematical text of South Asia dating back to the Vedic period, which primarily focused on the geometry of altar constructions for performing rituals. However, as PPD and I went through the pictorial databases of the Indus seals and pottery designs, we soon realized that many of the basic geometric constructions mentioned in the Vedic Sutras, such as the construction of a perfect square by the use of circles, must have already been known to the Indus civilization.
PPD’s ability to link the designs on artifacts belonging to various Bronze Age cultures (that have not left behind any texts or none that we can decipher) with mathematical knowledge suggested that there is an entire prehistory of mathematics waiting to be written. It is a lost body of knowledge that can only be inferred from the mathematical sophistication of the design motifs in the objects left behind by these cultures.
PPD’s later interest in Indian mathematics broadened to include the medieval era. As he gradually began focusing on the Kerala School of Mathematics that flourished between the 14th and 16th centuries and its pioneering figure Madhava, PPD became curious about the antecedents of what we now know as calculus. Being the rational scholar that he was, he refused to reduce his findings to simplistic, headline-grabbing rhetoric such as “Indians invented calculus centuries before Newton and Leibniz.” He was impervious to the politics of populist jingoism that has gradually pervaded Indian academia over the last decades. Rather, he came up with a very nuanced picture of what the scholars of the Kerala School had managed to achieve, presented brilliantly in his magnum opus The Mathematics of India (Springer, 2018). As he has made clear in his book and lectures, even if not immediately recognizable as the calculus of Newton and Leibniz, the work of these scholars is no less worthy of our appreciation.
Much of PPD’s later work that culminated in his 2018 book was done in the seclusion of his study in his Kochi apartment, where he spent the last decade and a half, barring occasional trips to academic institutes and conferences. On my occasional trips to Kochi, whenever I called PPD, he immediately invited me to visit, going so far as to arrange a car for traveling back and forth from his house. In his book-lined study, he would talk about what he was working on at the time, asking about goings on at IMSc and how our studies on the Indus inscriptions were moving forward. He would go on to give detailed reading suggestions to clear any doubts I may have mentioned about the development of mathematics.
He wore his enormous erudition lightly, never coming across as showing off but as a friend who guides you gently to some nugget of knowledge (a guru in the truest sense of the word, although I am not sure if PPD would have liked being referred to as one).
When I met him last in December 2022, he not only insisted on a meeting at his house and dinner afterwards, but also took us out the next morning to see the archaeological excavations at Pattanam, which has been identified as the port of Muziris referred to in Roman sources. On the way there, a discussion on the possible numbering system used by the Indus people somehow turned into a question about the first written evidence for a symbol indicating zero. PPD, in his usual manner, did not reduce it to a single sentence answer (for example, I have heard some immediately respond to this question with the statement “Bakshali manuscript”), but instead pointed out the question’s complexity to me, given the uncertainty of dates ascribed to the manuscripts, and how we may have to resort to epigraphic sources that clearly mention a regnal date. I remember this particularly because it so nicely encapsulates what for me was PPD’s quintessential style of discussion, that taught so much.
Earlier this year, when I had occasion to visit Kochi, I had called him – expecting yet another evening of delightful discussions. However, the voice at the other end no longer had the confident, jovial ring, pulsating with life, that I had always taken for granted. Haltingly, PPD explained to me that he had not been keeping well for some time and had just moved to an assisted care facility. He expressed hopes of seeing me again sometime in the near future when he was better. That was not to be as he passed away on 23rd August.
What would always remain with those whose lives he touched is the joy he exuded in learning and the magnanimity with which he shared his knowledge. In India, especially, retirement from an academic institution (and occasionally much earlier than that) is usually equated with intellectual atrophy. PPD showed me how one can begin a completely new chapter in their scholarly journey post-retirement, all the more so, by becoming one of the pre-eminent authorities on the topic. He lived the oft-heard but seldom practised motto of “Never stop learning.” Would that everyone were as fortunate!
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