This doesn't create a copy, it just provides a new version of the class which provides behavior for a contiguous submatrix of the big.matrix. Non-contiguous submatrices are not supported.

1 2 3 | ```
sub.big.matrix(x, firstRow = 1, lastRow = NULL,
firstCol = 1, lastCol = NULL, backingpath='' )
is.sub.big.matrix(x)
``` |

`x` |
either a |

`firstRow` |
the first row of the submatrix. |

`lastRow` |
the last row of the submatrix if not |

`firstCol` |
the first column of the submatrix. |

`lastCol` |
the last column of the submatrix if not |

`backingpath` |
required path to the filebacked object, if applicable. |

The `sub.big.matrix`

function allows a user to create a `big.matrix`

object that references a contiguous set of columns and rows of another
`big.matrix`

object.

The `is.sub.big.matrix`

function returns `TRUE`

if the specified
argument is a `sub.big.matrix`

object and return `FALSE`

otherwise.

A `big.matrix`

which is actually a submatrix of a larger `big.matrix`

.
It is not a physical copy. Only contiguous blocks may form a submatrix.

`big.matrix`

1 2 3 4 5 6 | ```
x <- big.matrix(10, 5, init=0, type="double")
x[,] <- 1:50
y <- sub.big.matrix(x, 2, 9, 2, 3)
y[,]
y[1,1] <- -99
x[,]
``` |

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