R: Triangular Matrices (Matlab Style)

tri {pracma} | R Documentation

## Triangular Matrices (Matlab Style)

### Description

Extract lower or upper triangular part of a matrix.

### Usage

    tril(M, k = 0)
    triu(M, k = 0)

### Arguments

`M` | numeric matrix.
`k` | integer, indicating a secondary diagonal.

### Details

`tril`
Returns the elements on and below the kth diagonal of X, where k = 0 is the main diagonal, k > 0 is above the main diagonal, and k < 0 is below the main diagonal.

`triu`
Returns the elements on and above the kth diagonal of X, where k = 0 is the main diagonal, k > 0 is above the main diagonal, and k < 0 is below the main diagonal.

### Value

Matrix the same size as the input matrix.

### Note

For `k==0` it is simply an application of the R functions `lower.tri` resp. `upper.tri`.

### See Also

`Diag`

### Examples

    tril(ones(4,4), +1)
    #    1  1  0  0
    #    1  1  1  0
    #    1  1  1  1
    #    1  1  1  1

    triu(ones(4,4), -1)
    #    1  1  1  1
    #    1  1  1  1
    #    0  1  1  1
    #    0  0  1  1

[Package pracma version 2.0.4 Index]