Person: Ibn Yusuf, Ahmed
Ahmed ibn Yusuf was an Islamic mathematician who wrote a commentary on Euclid's Elements which influenced later European mathematicians.
Mathematical Profile (Excerpt):
 Yusuf ibn Ibrahim lived in Baghdad but moved to Damascus in about 839.
 Yusuf ibn Ibrahim is known to have been a member of a group of scholars and this must have provided a strong intellectual environment for Ahmed.
 As well as a text on medicine, Yusuf is known to have written a work on astronomy and produced a collection of astronomical tables.
 Ahmed was to achieve an important role in Egypt and to understand this we must examine how Egypt achieved relative independence from the Abbasid Caliph.
 In 868 the Turkish general Babak was put in charge of Egypt and he chose to send his stepson Ahmad ibn Tulun there to take control.
 Ahmad ibn Tulun soon built up an army under his own control and managed to take control of the finances of the country.
 More importantly for Ahmed ibn Yusuf, the learning and scholarship of Baghdad was encouraged in Egypt, and he was able to pursue his mathematical researches while working for the Tulunid dynasty.
 We know of a work by Ahmed on ratio and proportion, a book On similar arcs, a commentary on Ptolemy's Centiloquium and a book about the astrolabe.
 All these works have survived and historians are confident that they are indeed the work of Ahmed, but several other works which some claim to be due to him are probably by other authors.
 Ahmed's work on ratio and proportion was translated into Latin by Gherard of Cremona.
 However it was not without its defects and Campanus of Novara pointed out a circular argument which occurs in Ahmed's reasoning.
 In the treatise Ahmed proves that similar arcs of circles can be equal and not equal.
 Ahmed ibn Yusuf also gave methods to solve tax problems which appear in Fibonacci's Liber Abaci.
Born 835, Baghdad (now in Iraq). Died 912, Cairo, Egypt.
View full biography at MacTutor
Tags relevant for this person:
Ancient Arab, Astronomy, Origin Iraq
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Epochs: 1
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References
Adapted from other CC BYSA 4.0 Sources:
 O’Connor, John J; Robertson, Edmund F: MacTutor History of Mathematics Archive