Matrix (version 1.0-4)

spMatrix: Sparse Matrix Constructor From Triplet

Description

User friendly construction of a sparse matrix (inheriting from class TsparseMatrix) from the triplet representation.

Usage

spMatrix(nrow, ncol, i = integer(), j = integer(), x = numeric())

Arguments

nrow, ncol

integers specifying the desired number of rows and columns.

i,j

integer vectors of the same length specifying the locations of the non-zero (or non-TRUE) entries of the matrix.

x

atomic vector of the same length as i and j, specifying the values of the non-zero entries.

Value

• A sparse matrix in triplet form, as an Robject inheriting from both TsparseMatrix and generalMatrix.

  The matrix $M$ will have M[i[k], j[k]] == x[k], for $k = 1,2,\ldots, n$, where n = length(i) and M[ i', j' ] == 0 for all other pairs $(i',j')$.

See Also

Matrix(*, sparse=TRUE) for the more usual constructor of such matrices; similarly, sparseMatrix which is a bit more general than spMatrix() and returns a CsparseMatrix which is often slightly more desirable. Further, bdiag and Diagonal for (block-)diagonal matrix constructors.

Consider TsparseMatrix and similar class definition help files.

Examples

## simple example
A <- spMatrix(10,20, i = c(1,3:8),
                     j = c(2,9,6:10),
                     x = 7 * (1:7))
A # a "dgTMatrix"
summary(A)
str(A) # note that *internally* 0-based indices (i,j) are used

L <- spMatrix(9, 30, i = rep(1:9, 3), 1:27,
              (1:27) %% 4 != 1)
L # an "lgTMatrix"

### This is a useful utility, to be used for experiments :

 rSpMatrix <- function(nrow, ncol, nnz,
                       rand.x = function(n) round(rnorm(nnz), 2))
 {
     ## Purpose: random sparse matrix
     ## --------------------------------------------------------------
     ## Arguments: (nrow,ncol): dimension
     ##          nnz  :  number of non-zero entries
     ##         rand.x:  random number generator for 'x' slot
     ## --------------------------------------------------------------
     ## Author: Martin Maechler, Date: 14.-16. May 2007
     stopifnot((nnz <- as.integer(nnz)) >= 0,
               nrow >= 0, ncol >= 0,
               nnz <= nrow * ncol)
     spMatrix(nrow, ncol,
              i = sample(nrow, nnz, replace = TRUE),
              j = sample(ncol, nnz, replace = TRUE),
              x = rand.x(nnz))
 }

 M1 <- rSpMatrix(100000, 20, nnz = 200)
 summary(M1)