Indian classical music is based on the ragas ("colors"), which are scales and melodies that provide the foundation for a performance. Unlike western classical music, that is deterministic, Indian classical music allows for a much greater degree of "personalization" of the performance, almost to the level of jazz-like improvisation. Thus, each performance of a raga is different. The goal of the raga is to create a trancey state, to broadcast a mood of ecstasy. The main difference with western classical music is that the Indian ragas are not "composed" by a composer, but were created via a lengthy evolutionary process over the centuries. Thus they do not represent mind of the composer but a universal idea of the world. They transmit not personal but impersonal emotion. Another difference is that Indian music is monodic, not polyphonic. Hindustani (North Indian) ragas are assigned to specific times of the day (or night) and to specific seasons. Many ragas share the same scale, and many ragas share the same melodic theme. There are thousands of ragas, but six are considered fundamental: Bhairav, Malkauns, Hindol, Dipak, Megh and Shree. A raga is not necessarily instrumental, and, if vocal, it is not necessarily accompanied. But when it is accompanied by percussion (such as tablas), the rhythm is often rather intricate because it si constructed from a combination of fundamental rhythmic patterns (or talas). The main instrument of the ragas is the sitar, although historically the vina zither was at least equally important. Carnatic (Southern Indian) ragas constitute one of the oldest systems of music in the world. They are based on seven rhythmic cycles and 72 fundamental ragas. The founder of the Karnataka school is considered to be Purandara Dasa (1494). Carnatic music is mostly vocal and devotional in nature, and played with different instruments than Hindustani music (such as the mridangam drum, the ghatam clay pot, the vina sitar as opposed to sitar, sarod, tambura and tabla). The fundamental format of Carnatic songs is the "kriti", which are usually set in the style of a raga (the raga serves as the melodic foundation). The golden age of Carnatic music was the age of Syama Sastri, who died in 1827, of Tyagaraja, who died in 1847 and who composed the Pancharatna Krithis as well as two "operas", Prahalada Bhakti Vijayam and Nauca Charitam, and of Muthuswami Dikshitar, who died in 1835 after composing the Kamalamba Navavarnams and the Navagraha krithis.