Structured arrays are vectors, matrices and arrays with special structure that allows for efficient specification and representation as well as efficient computation. Structured arrays complement packed arrays (arrays with single type for all elements) and sparse arrays (arrays where most elements are zero). Structured arrays occur in all computational domains and typically enable efficiency breakthroughs years or decades before general unstructured arrays can tackle the same problem. The Wolfram Language provides a convenient specification and representation for the structured arrays that often occur in applications, as well as optimized algorithms for performing operations on them, such as linear solving, inversion and eigenvalue computations.
PermutationMatrix — permutation matrices
SymmetrizedArray — structured representation of symmetric arrays
Normal — convert structured arrays to lists
QuantityArray — represent an array of quantities