Strassen algorithm

Not to be confused with the Schönhage–Strassen algorithm for multiplication of polynomials.

In linear algebra, the Strassen algorithm, named after Volker Strassen, is an algorithm for matrix multiplication. It is faster than the standard matrix multiplication algorithm for large matrices, with a better asymptotic complexity ($O(n^{\log _{2}7})$ versus $O(n^{3})$), although the naive algorithm is often better for smaller matrices. The Strassen algorithm is slower than the fastest known algorithms for extremely large matrices, but such galactic algorithms are not useful in practice, as they are much slower for matrices of practical size. For small matrices, highly optimized implementations of the conventional algorithm are generally faster because Strassen's additional additions and recursion overhead outweigh its reduction in multiplications.

Strassen's algorithm works for any ring such as plus/multiply, but not all semirings, particularly combinatorial matrix multiplication such as min-plus or boolean algebra, where the naive algorithm still works.