The sparse Matrices - Maple Help

The sparse Matrices

Description

 • A sparse matrix has the property that only nonzero elements are stored in the underlying data structure.
 • Sparse storage can be used to construct a Matrix, Vector, or Array, and the sparse indexing function can be used to construct a table or array(deprecated).
 • Ignoring semi-sparse rtable data structures like triangular[upper], and band, there are two sparse formats used by rtables.
 The first is identical to the table format, and is only used when the datatype is a non-hardware type.
 The second format is always used when the datatype is a hardware numeric type, and matches the format used by the NAG numerical algorithms.  The NAG sparse format has N index vectors and one data vector for a N-dimensional Matrix. Thus, a 2-D sparse rtable with datatype=float[8] will have two integer index vectors, v1, and v2, plus a vector of 64-bit hardware float data. If v1[0] = 1, and v2[0] = 2, then the index [1,2] will retrieve the element stored at the first position of the data vector.
 • The sparse indexing function specifies that unassigned entries of a table or an array have the value 0. For example, array(sparse, 1..2, 1..2) is a zero matrix.
 • If T is a table and j is an unevaluated name, then T[j] returns unevaluated. However, if j evaluates to an integer, then T[j] returns either the value of T[j] or 0 if T[j] has no assigned value.

Examples

 > $M≔\mathrm{Matrix}\left(3,3,\mathrm{storage}=\mathrm{sparse}\right)$
 ${M}{:=}\left[\begin{array}{rrr}{0}& {0}& {0}\\ {0}& {0}& {0}\\ {0}& {0}& {0}\end{array}\right]$ (1)
 > ${M}_{1,1}$
 ${0}$ (2)
 > $T≔\mathrm{table}\left(\mathrm{sparse},\left[A=a\right]\right):$
 > ${T}_{A}$
 ${a}$ (3)
 > ${T}_{B}$
 ${0}$ (4)
 > $a≔\mathrm{array}\left(\mathrm{sparse},1..2\right):$
 > ${a}_{1}$
 ${0}$ (5)
 > ${a}_{j}$
 ${{a}}_{{j}}$ (6)