My thesis entailed enhancing a large program called SCHUR, named after the Issai Schur (1875-1941). SCHUR provided a computational environment where the entities being manipulated were partitions. The partitions on N is the list of ways N items can be grouped. For example, three items can be partitioned as {1, 1, 1}, {2, 1} and {3}. SCHUR actually manipulated lists of weighted partitions, like
{4, 1} + 3{3, 2} - 2{2, 1, 1}and defined a number of operators on these lists. As well as simple addition and subtraction, I recall there were also inner and outer products and the delightful plethysm. I spent a reasonably happy year puttering around within SCHUR adding a number of features (like that damn plethysm operator, which I recall as being horribly complex). SCHUR was (and is still?) a tool for theoretical Physicists in the same way that I imagine MatLab or Mathematica are.
The main thing is, it got me a degree and a career,