# spMatrix: Sparse Matrix Constructor From Triplet In Matrix: Sparse and Dense Matrix Classes and Methods

 spMatrix R Documentation

## Sparse Matrix Constructor From Triplet

### Description

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

This is much less flexible than `sparseMatrix()` and hence somewhat deprecated.

### Usage

```spMatrix(nrow, ncol, i = integer(), j = integer(), x = double())
```

### 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 R object inheriting from both `TsparseMatrix` and `generalMatrix`.

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

`Matrix(*, sparse=TRUE)` for the more usual constructor of such matrices. Then, `sparseMatrix` is more general and flexible than `spMatrix()` and by default 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"

## A simplified predecessor of  Matrix'  rsparsematrix() function :

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)
```

Matrix documentation built on Nov. 11, 2022, 9:06 a.m.