ArrayRules[SparseArray[...]] gives the rules {pos_1 -> val_1, pos_2 -> val_2, ...} specifying elements in a sparse array. ArrayRules[list] gives rules for SparseArray[list].

Ways to get pieces of matrices. Matrices in Mathematica are represented as lists of lists. You can use all the standard Mathematica list-manipulation operations on matrices. ...

Many large-scale applications of linear algebra involve matrices that have many elements, but comparatively few that are nonzero. You can represent such sparse matrices ...

Mathematica automatically handles both numeric and symbolic matrices, seamlessly switching among large numbers of highly-optimized algorithms. Using many original methods, ...

Mathematica has special sparse-array technology for efficiently handling arrays with literally astronomical numbers of elements when only a small fraction of the elements are ...

Integrated into the Mathematica system are powerful functions for analyzing large volumes of discrete and integer data—often conveniently specified using Mathematica's ...

Mathematica provides a carefully chosen set of functions for accessing elements of lists either using indices or positions, or using patterns or criteria for their values.

Mathematica provides several convenient methods for extracting and manipulating parts of matrices. The flexible [[ ]] (Part) and ;; (Span) syntaxes provide compact yet ...

EdgeRules[g] gives the list of edge rules for the graph g.

SparseArray[{pos_1 -> val_1, pos_2 -> val_2, ...}] yields a sparse array in which values val_i appear at positions pos_i. SparseArray[{pos_1, pos_2, ...} -> {val_1, val_2, ...