# Matrix

##### Construct a Classed Matrix

Construct a Matrix of a class that inherits from `Matrix`

.

##### Usage

```
Matrix(data=NA, nrow=1, ncol=1, byrow=FALSE, dimnames=NULL,
sparse = NULL, doDiag = TRUE, forceCheck = FALSE)
```

##### Arguments

- data
an optional numeric data vector or matrix.

- nrow
when

`data`

is not a matrix, the desired number of rows- ncol
when

`data`

is not a matrix, the desired number of columns- byrow
logical. If

`FALSE`

(the default) the matrix is filled by columns, otherwise the matrix is filled by rows.- dimnames
a

`dimnames`

attribute for the matrix: a`list`

of two character components. They are set if not`NULL`

(as per default).- sparse
logical or

`NULL`

, specifying if the result should be sparse or not. By default, it is made sparse when more than half of the entries are 0.Note that when the resulting matrix is diagonal (“mathematically”),

`sparse=FALSE`

results in a`'>diagonalMatrix`

, unless`doDiag=FALSE`

as well, see the first examples.- doDiag
only when

`sparse = FALSE`

, logical indicating if a`'>diagonalMatrix`

object should be considered (default). Otherwise, in such a case, a dense (symmetric) matrix will be returned.- forceCheck
logical indicating if the checks for structure should even happen when

`data`

is already a`"Matrix"`

object.

##### Details

If either of `nrow`

or `ncol`

is not given, an attempt is
made to infer it from the length of `data`

and the other
parameter.
Further, `Matrix()`

makes efforts to keep `logical`

matrices logical, i.e., inheriting from class `'>lMatrix`

,
and to determine specially structured matrices such as symmetric,
triangular or diagonal ones. Note that a *symmetric* matrix also
needs symmetric `dimnames`

, e.g., by specifying
`dimnames = list(NULL,NULL)`

, see the examples.

Most of the time, the function works via a traditional (*full*)
`matrix`

. However, `Matrix(0, nrow,ncol)`

directly
constructs an “empty” '>sparseMatrix, as does
`Matrix(FALSE, *)`

.

Although it is sometime possible to mix unclassed matrices (created
with `matrix`

) with ones of class `"Matrix"`

, it is much
safer to always use carefully constructed ones of class
`"Matrix"`

.

##### Value

Returns matrix of a class that inherits from `"Matrix"`

.
Only if `data`

is not a `matrix`

and does not already inherit
from class `'>Matrix`

are the arguments
`nrow`

, `ncol`

and `byrow`

made use of.

##### See Also

The classes `'>Matrix`

,
`'>symmetricMatrix`

,
`'>triangularMatrix`

, and
`'>diagonalMatrix`

; further,
`matrix`

.

Special matrices can be constructed, e.g., via
`sparseMatrix`

(sparse), `bdiag`

(block-diagonal), `bandSparse`

(banded sparse), or
`Diagonal`

.

##### Examples

```
# NOT RUN {
Matrix(0, 3, 2) # 3 by 2 matrix of zeros -> sparse
Matrix(0, 3, 2, sparse=FALSE)# -> 'dense'
Matrix(0, 2, 2, sparse=FALSE)# diagonal !
Matrix(0, 2, 2, sparse=FALSE, doDiag=FALSE)# -> dense
Matrix(1:6, 3, 2) # a 3 by 2 matrix (+ integer warning)
Matrix(1:6 + 1, nrow=3)
## logical ones:
Matrix(diag(4) > 0)# -> "ldiMatrix" with diag = "U"
Matrix(diag(4) > 0, sparse=TRUE)# -> sparse...
Matrix(diag(4) >= 0)# -> "lsyMatrix" (of all 'TRUE')
## triangular
l3 <- upper.tri(matrix(,3,3))
(M <- Matrix(l3)) # -> "ltCMatrix"
Matrix(! l3)# -> "ltrMatrix"
as(l3, "CsparseMatrix")
Matrix(1:9, nrow=3,
dimnames = list(c("a", "b", "c"), c("A", "B", "C")))
(I3 <- Matrix(diag(3)))# identity, i.e., unit "diagonalMatrix"
str(I3) # note the empty 'x' slot
(A <- cbind(a=c(2,1), b=1:2))# symmetric *apart* from dimnames
Matrix(A) # hence 'dgeMatrix'
(As <- Matrix(A, dimnames = list(NULL,NULL)))# -> symmetric
stopifnot(is(As, "symmetricMatrix"),
is(Matrix(0, 3,3), "sparseMatrix"),
is(Matrix(FALSE, 1,1), "sparseMatrix"))
# }
```

*Documentation reproduced from package Matrix, version 1.2-18, License: GPL (>= 2) | file LICENCE*