

A mathematician whose monumental textbook on complex functions shaped the education of a generation of British analysts.
Andrew Forsyth emerged from the rigorous mathematical culture of late Victorian Britain, carving a path that would influence the field for decades. As a student at Trinity College, Cambridge, he fell under the spell of the theory of functions, a passion that defined his career. His magnum opus, 'Theory of Functions of a Complex Variable', was not merely a book but a sprawling, six-volume landscape that attempted to map the entire territory of the subject. Its sheer ambition and encyclopedic scope made it a standard reference, though its density also earned it a reputation for being formidable. Forsyth held prestigious chairs, first at Liverpool and then at Imperial College London, before succeeding the great George Stokes at Cambridge. His later years were marked by a controversial and ultimately unsuccessful attempt to develop a new theory of differential equations, a project that consumed him but left his legacy firmly anchored in that earlier, monumental work.
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He was a notable 'Apostle', a member of the Cambridge Conversazione Society, an elite secret debating club.
His massive textbook was famously difficult; a contemporary mathematician joked that reviewing it would be 'like reviewing the Alps'.
He resigned his Cambridge chair in 1910 to get married, as the position required fellows to remain unmarried at the time.
“The theory of functions is the true life of mathematics.”