Jyeṣṭhadeva

Jyeṣṭhadeva () was an astronomer-mathematician of the Kerala school of astronomy and mathematics founded by Madhava of Sangamagrama (). He is best known as the author of the Yuktibhāṣā, a commentary in Malayalam of the treatise Tantrasamgraha by Nilakantha Somayaji. In the Yuktibhāṣā, Jyeṣṭhadeva gave complete proofs and rationales for the statements in Tantrasamgraha, which was unusual for traditional Indian mathematicians of the time. The Yuktibhāṣā is now believed to contain derivations of Taylor and infinite series expansions for certain trigonometric functions. However, it did not combine several ideas under the unifying concepts of the derivative and the integral, show the connection between the two, or turn calculus into the powerful problem-solving tool we have today. Jyeṣṭhadeva also authored Drk-karana, a treatise on astronomical observations.

==Life period of Jyeṣṭhadeva== There are a few references to Jyeṣṭhadeva scattered across several old manuscripts. From these manuscripts, one can deduce a few bare facts about the life of Jyeṣṭhadeva. He was a Nambudiri belonging to the Parangngottu family (Sanskritised as Parakroda) born about the year 1500 CE. He was a pupil of Damodara and a younger contemporary of Nilakantha Somayaji. Acyuta Piṣāraṭi was a pupil of Jyeṣṭhadeva. In the concluding verse of his work Uparagakriyakrama, completed in 1592, Piṣāraṭi referred to Jyeṣṭhadeva as his "aged benign teacher". From a few references in Drk-karana, a work believed to be of Jyeṣṭhadeva, one may conclude that Jyeṣṭhadeva lived up to about 1610 CE. According to K. V. Sarma, the name "Jyeṣṭhadeva" is most probably the Sanskritised form of his personal name in the local language Malayalam.