# Ahmad ibn Yusuf

**Abu Ja'far Ahmad ibn Yusuf ibn Ibrahim ibn Tammam al-Siddiq Al-Baghdadi** (835–912), known in the West by his Latinized name **Hametus**, was an Arab mathematician, like his father Yusuf ibn Ibrahim (Arabic: يوسف بن ابراهيم الصدَيق البغدادي ).

## Life

Ahmad ibn Yusuf was born in Baghdad and moved with his father to Damascus in 839. He later moved to Cairo, but the exact date is unknown: since he was also known as *al-Misri*, which means *the Egyptian*, this probably happened at an early age. Eventually, he also died in Cairo. He probably grew up in a strongly intellectual environment: his father worked on Mathematics, Astronomy and Medicine, produced astronomical tables and was a member of a group of scholars. He achieved an important role in Egypt, which was caused by Egypt's relative independence from the Abbasid Caliph.

## Work

In some of the works attributed to Ahmad, it is not clear if the text came from him, his father, or whether they wrote together. It is clear, however, that he worked on a book on ratio and proportion. This was translated to Latin by Gherard of Cremona and was a commentary of Euclid's *Elements*. This book influenced early European mathematicians such as Fibonacci. Further, in *On similar arcs*, he commented on Ptolemy's *Karpos* (or *Centiloquium*); many scholars believe that ibn Yusuf was in fact the true author of that work.^{[1]} He also wrote a book on the astrolabe. He invented methods to solve tax problems that were later presented in Fibonacci's *Liber Abaci*. He was also quoted by mathematicians such as Thomas Bradwardine, Jordanus de Nemore and Luca Pacioli.

## See also

## Notes

- ↑ Richard Lemay, Origin and success of the
*Kitab Thamara*of Abu Ja'far Ahmad ibn Yusuf, in*Proceedings of the 1st International Symposium for the History of Arabic Science, University of Aleppo (1976)*, Aleppo 1978

- M Steinschneider, Yusuf ben Ibrahim und Ahmad ibn Yusuf, Bibliotheca mathematic (1888), 49–117.
- Schrader, Dorothy (1970). "Aḥmad Ibn Yūsef".
*Dictionary of Scientific Biography*.**1**. New York: Charles Scribner's Sons. pp. 82–83. ISBN 0-684-10114-9. - H. L. L. Busard and P. S. van Koningsveld,
*Der "Liber de arcubus similibus" des Ahmad ibn Jusuf*, Annals of science**30**(1973), 381–406. - M Steinschneider, Yusuf ben Ibrahim und Ahmad ibn Yusuf, Bibliotheca mathematic (1888), 49–117.

## External links

- O'Connor, John J.; Robertson, Edmund F., "Ahmad ibn Yusuf",
*MacTutor History of Mathematics archive*, University of St Andrews. - Schrader, Dorothy V. (2008) [1970–80]. "Aḥmad Ibn Yūsuf".
*Complete Dictionary of Scientific Biography*. Encyclopedia.com.