Lalla (c. 720–790 CE) was an Indian mathematician, astronomer, and astrologer who belonged to a family of astronomers. Lalla was the son of Trivikrama Bhatta and the grandson of Śâmba, and he lived in central India, possibly in the Lāṭa region in modern south Gujarat. Lalla was known as being one of the leading Indian astronomers during the eighth century. Only two of Lalla's works are currently thought to be extant.
His most famous work was titled Śiṣya-dhī-vṛddhida-tantra, or "Treatise which expands the intellect of students." This text is one of the first major Sanskrit astronomical texts known from the period following the 7th-century works of Brahmagupta and Bhāskara I. It generally treats the same astronomical subject matter and demonstrates the same computational techniques as earlier authors, although there are some significant innovations, such that Lalla’s treatise offers a compromise between the rival astronomical schools of his predecessors, Āryabhaṭa I and Brahmagupta. Although Lalla is known to be a follower of Āryabhaṭa, he combines techniques from both. It is within "Śiṣyadhīv ṛddhidatantra" that the earliest known description of a perpetuum mobile is described.
Lalla's other works such as his text, " Jyotiṣaratnakośa" or "Treasury of Jewels", is his treatise on catarchic astrology. This work is one of the earliest known Sanskrit astrological works for determining auspicious and inauspicious times. No edition of this text has ever been published while the known manuscripts are incomplete.
In his work, Lalla drew on his predecessors Āryabhaṭa, Brahmagupta, and Bhāskara I. In turn, he influenced later generations of astronomers, including Śrīpati, Vaṭeśvara, and Bhāskara II (who later wrote a commentary on the Śiṣyadhīvṛddhidatantra).
He followed the Ārya-pakṣa or the school of Āryabhaṭa (continued by Bhāskara I), but divided the mahāyuga the traditional way, following the Brāhma-pakṣa school of Brahmagupta. Although he followed Āryabhaṭa, he did not believe in the rotation of the Earth.
- Śiṣyadhīvṛddhidatantra. The most extensive extant exposition of the views of the Āryapaksa school. It contains twenty-two chapters divided into two books:
"I. On the computation of the positions of the planets.
1. On the mean longitudes of the planets.
2. On the true longitudes of the planets.
3. On the three problems involving diurnal motion.
4. On lunar eclipses.
5. On solar eclipses.
6. On the syzygies.
7. On the heliacal settings and risings of the planets.
8. On the shadow of the moon.
9. On the lunar crescent.
10. On planetary conjunctions.
11. On conjunctions of the planets with the stars.
12. On the pātas of the sun and moon.
II. On the Sphere.
1. On graphical representations.
2. On the construction of the celestial sphere.
3. On the principles of mean motion.
4. On the terrestrial sphere.
5. On the motions and stations of the planets.
6. On geography.
7. On erroneous knowledge.
8. On instruments.
9. On certain (selected) problems"
- Jyotiṣaratnakośa. Most popular astronomy book in India for 300 years.
- A commentary on Brahmagupta's Khandakhadyaka, now lost