Itzḥak ben Shlomo ibn al-Aḥdab (or ibn al-Ḥadib) ben Tzaddiq ha-Sefardi (Hebrew: יצחק בן שלמה בן צדיק אלאחדב הספרדי, c. 1350 – c. 1426) was a Jewish mathematician, astronomer, and poet.
[4][5] His astronomical works include Oraḥ selulah (Upraised Path), a set of tables in Hebrew for conjunctions and oppositions of the Sun and the Moon,[6] Keli Ḥemdah (Precious Instrument), which describes a unique equatorium of his own invention, functioning on the Ptolemaic theory of epicycles,[7] and Keli Memutsa (Intermediate Instrument), which describes another unique instrument of his own design, a combination astrolabe-quadrant.
[7] Oraḥ selulah survives in 25 MSS, Keli Ḥemdah in 15 MSS, and Keli Memutsa in 1 MS.[8] He is the author of a commentary on the Passover Haggadah, titled Pesach Doros (Passover of later generations) and printed by Mekhon Bet Aharon ṿe-Yiśraʼel in 2000.
[8] Leshon ha-Zahav (Golden Language), an explication of the names for units and measurements found in the Hebrew Bible.
[8] He also wrote songs, published as Shirei Rabbeinu Itzḥak ben Shlomo ibn al-Aḥdab (1987).