(Διόφαντος), of Alexandria, the only Greek writer on Algebra. His period is wholly unknown, which is not to be wondered at if we consider that he stands quite alone as to the subject which he treated. But, looking at the improbability of all mention of such a writer being omitted by Proclus and Pappus, we feel strongly inclined to place him towards the end of the fifth century of our era at the earliest. If the Diophantus, on whose astronomical work (according to Suidas) Hypatia wrote a commentary, and whose arithmetic Theon mentions in his commentary on the Almagest, be the subject of our article, he must have lived before the fifth century: but it would be by no means safe to assume this identity. Abulpharagius, according to Montucla, places him at A. D. 365. The first writer who mentions him, (if it be not Theon) is John, patriarch of Jerusalem, in his life of Johannes Damascenus, written in the eighth century. It matters not much where we place him, as far as Greek literature is concerned: the question will only become of importance when we have the means of investigating whether or not he derived his algebra, or any of it, from an Indian source. Colebrooke, as to this matter, is content that Diophantus should be placed in the fourth century. (See the Penny Cyclopaedia, art. Viya Ganita.)
It is singular that, though his date is uncertain to a couple of centuries at least, we have some reason to suppose that he married at the age of 33, and that in five years a son was born of this marriage, who died at the age of 42, four years before his father: so that Diophantus lived to 84. Bachet, his editor, found a problem proposed in verse, in an unpublished Greek anthology, like some of those which Diophantus himself proposed in verse, and composed in the manner of an epitaph. The unknown quantity is the age to which Diophantus lived, and the simple equation of condition to which it leads gives, when solved, the preceding information. But it is just as likely as not that the maker of the epigram invented the dates.
[A. De M.]