View source for Biography:Ahmad ibn Yusuf

{{Short description|Arab mathematician}}
'''Abu Ja'far Ahmad ibn Yusuf ibn Ibrahim ibn Tammam al-Siddiq Al-Baghdadi''' ({{lang-ar|أبو جعفر أحمد بن يوسف بن ابراهيم بن تمام الصديق البغدادي}}; 835–912), known in the West by his Latinized name '''Hametus''', was a [[Religion:Muslim|Muslim]] Arab [[Biography:Mathematician|mathematician]], like his father Yusuf ibn Ibrahim ({{lang-ar|يوسف بن ابراهيم الصدَيق البغدادي }}).

== Life ==
Ahmad ibn Yusuf was born in [[Place:Baghdad|Baghdad]] and moved with his father to [[Place:Damascus|Damascus]] in 839. He later moved to [[Place:Cairo|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:Astronomy|Astronomy]] and [[Medicine:Medicine|Medicine]], produced astronomical tables and was a member of a group of scholars. He achieved an important role in [[Place:Egypt|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|ratio]] and [[Proportionality (mathematics)|proportion]]. This was translated to Latin by Gherard of Cremona and was a commentary of [[Biography:Euclid|Euclid]]'s ''Elements''. This book influenced early European mathematicians such as Fibonacci. Further, in ''On similar arcs'', he commented on [[Biography:Ptolemy|Ptolemy]]'s ''Karpos'' (or ''[[Unsolved:Centiloquium|Centiloquium]]''); many scholars believe that ibn Yusuf was in fact the true author of that work.<ref>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</ref>  He also wrote a book on the [[Astronomy:Astrolabe|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 [[Biography:Thomas Bradwardine|Thomas Bradwardine]], [[Biography:Jordanus de Nemore|Jordanus de Nemore]] and [[Biography:Luca Pacioli|Luca Pacioli]].

==See also==
*List of Arab scientists and scholars

==Notes==
{{reflist}}

* {{cite encyclopedia | last =Schrader | first =Dorothy | title =Aḥmad Ibn Yūsef | encyclopedia = Dictionary of Scientific Biography | volume = 1 | pages =82–83 | publisher = Charles Scribner's Sons | location = New York | date = 1970 | 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==
* {{MacTutor Biography|id=Ahmad}}
* {{cite encyclopedia | last =  Schrader | first = Dorothy V. | title=Aḥmad Ibn Yūsuf  | url=http://www.encyclopedia.com/doc/1G2-2830900059.html |  encyclopedia = Complete Dictionary of Scientific Biography | publisher = [[Encyclopedia.com]] | orig-year=1970–80 | date = 2008 }}

{{Islamic mathematics}}


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[[Category:9th-century mathematicians]]
[[Category:10th-century mathematicians]]

{{Sourceattribution|Ahmad ibn Yusuf}}