sdiag {mgcv} | R Documentation |

## Extract or modify diagonals of a matrix

### Description

Extracts or modifies sub- or super- diagonals of a matrix.

### Usage

```
sdiag(A,k=0)
sdiag(A,k=0) <- value
```

### Arguments

`A` |
a matrix |

`k` |
sub- (negative) or super- (positive) diagonal of a matrix. 0 is the leading diagonal. |

`value` |
single value, or vector of the same length as the diagonal. |

### Value

A vector containing the requested diagonal, or a matrix with the requested diagonal replaced by `value`

.

### Author(s)

Simon N. Wood simon.wood@r-project.org

### Examples

```
require(mgcv)
A <- matrix(1:35,7,5)
A
sdiag(A,1) ## first super diagonal
sdiag(A,-1) ## first sub diagonal
sdiag(A) <- 1 ## leading diagonal set to 1
sdiag(A,3) <- c(-1,-2) ## set 3rd super diagonal
```

[Package

*mgcv*version 1.9-0 Index]