Which South Indian poet and composer has a school of music where Sooryakantam  is called Chāyāvati ?
Muthuswami Dikshitar Muthuswami Dikshitar (March 24, 1775 – October 21, 1835) was a South Indian poet and composer and is one of the Musical Trinity of Carnatic music. His compositions, of which around 500 are commonly known, are noted for their contemplative nature and for capturing the essence of the raga forms through the vainika (veena) style that emphasises gamakas. They are typically in a slower speed (chowka kala). He is also known by his signature name of Guruguha which is also his mudra (can be found in every one of his songs). His compositions are widely sung and played in classical concerts of Carnatic music.
Melpathur Narayana Bhattathiri Melpathur Narayana Bhattathiri (Malayalam: മേല്പത്തൂർ നാരായണ ഭട്ടതിരി ; 1560–1646/1666), third student of Achyuta Pisharati, was a member of Madhava of Sangamagrama's Kerala school of astronomy and mathematics. He was a mathematical linguist (vyakarana). His most important scholarly work, "Prkriya-sarvawom", sets forth an axiomatic system elaborating on the classical system of Panini. However, he is most famous for his masterpiece, "Narayaneeyam", a devotional composition in praise of Guruvayoorappan (Krishna) that is still sung at Guruvayoor Temple.