Mistress of Girton whose mathematical work formed the basis of chaos theory

DAME Mary Cartwright, who has died aged 97, was one of most eminent British mathematicians of the century, and between 1949 and 1968 Mistress of Girton College, Cambridge - the longest tenure in the college's history.

Mary Lucy Cartwright was born on December 17 1900 at Aynho, Northamptonshire, where her father was curate and later rector. At first educated by governesses, Mary was later sent away to various schools, including Godolphin, in Salisbury. Her younger brother Frederick, a Rugbeian, would end his career as deputy chairman of the British Steel Corp-oration.

In 1919 Mary Cartwright went up to St Hugh's College, Oxford, to read mathematics. Owing to the gaps in her schooling she felt herself ill-prepared for the course, and in 1921 obtained only a Second in Moderations. Tempted to change to history, she rejected this option because it seemed to entail rather too much work.

Her breakthrough as a mathematician came in her third year, when V C Morton, later professor of mathematics at Aberystwyth, suggested at a party on a barge in Eights Week that she should attend evening classes of the great G H Hardy, then Savilian Professor of Geometry. Mary Cartwright went on to obtain a First in 1923, only the second year in which women took Final degrees at Oxford.

On coming down, she became a schoolmistress, first at Alice Ottley School, Worcester, and then at Wycombe Abbey. But in 1928 she returned to Oxford to work as a student of G H Hardy, who had been highly impressed by her work. "Let's see," he said when she produced an obviously fallacious result, "there's always hope when you get a sharp contradiction."

In 1930 Mary Cartwright obtained a doctorate for her thesis on The Zeros of Integral Functions of Special Types, and moved to Girton College, Cambridge, where, financed by a Yarrow Research Fellowhip, she continued to work on the theory of functions.

The important results she obtained, published in 1935 in the Mathematische Annalen, prompted G H Hardy (who had moved to Cambridge in 1931) and J E Littlewood to recommend her for an Assistant Lectureship. She became Lecturer in 1935, and Reader in the Theory of Functions in 1959. At Girton she was director of studies in mathematics.

In 1939 the Department of Scientific and Industrial Research asked Mary Cartwright to help in solving "certain very objectionable-looking differential equations occurring in connection with radar". She undertook this work in partnership with Littlewood, who described her as "the only woman in my life to whom I have written twice in one day". The results they obtained on the periodicity and stability of solutions of non-linear differential equations form the basis for the modern theory of dynamical systems and chaos.

In 1947 Mary Cartwright became the first woman mathematician to be elected to the Royal Society. But the focus of her life changed dramatically in 1949 when she was appointed Mistress of Girton, which had only been fully incorporated into Cambridge University the year before.

She provided quiet, unassuming and clear-headed leadership of the college during a time of many changes. Though obliged to spend long hours in committee, she always found time to interview entrance candidates - in batches of five, lumped together quite irrespective of the subject for which they were applying.

Inevitably she was no longer able to devote herself wholeheartedly to mathematics, but she did not seem to regret this, believing the subject to be predominately a young person's game. Even so, honours continued to be heaped upon her. The Royal Society bestowed its Sylvester Medal in 1964; and four years later the London Mathematical Society, of which she had been President from 1961 to 1963, awarded her its De Morgan Medal.

She was appointed DBE in 1969.

In retirement, Mary Cartwright held visiting professorships in a number of American and European universities. But her base remained in Cambridge, where she concentrated on editing the manuscripts of Hardy and Littlewood.

As the years went by she seemed to lose some of her shyness, and at lunch in Girton enjoyed regaling the younger fellows with stories from her academic travels.