A small random sample of rows/columns of any matrix is a decent proxy for the matrix, provided sampling probabilities are proportional to squared lengths.

Web search has come a long way from matching query words with document words.  It is now mediated by knowledge graphs (KGs) such as Freebase, having hundreds of millions of entities belonging to tens of thousands of types, connected by billions of

Poisson processes are frequently used, e.g. to model the customer arrival process in service systems, or the claim arrival proces in insurance models.

The complexity of Iterated Matrix Multiplication is a central theme in Computational Complexity theory, as the problem is closely related to the problem of separating various complexity classes within $P$.

Garbled circuits are a central primitive in cryptography. Intuitively, a garbled circuit enables its holder to evaluate a circuit on an input, so that the evaluator learns the output but learns nothing about the circuit or the input.