Null {MASS} | R Documentation

## Null Spaces of Matrices

### Description

Given a matrix, `M`, find a matrix `N` giving a basis for the null space. That is `t(N) %*% M` is the zero and `N` has the maximum number of linearly independent columns.

### Usage

    Null(M)

### Arguments

`M` | Input matrix. A vector is coerced to a 1-column matrix.

### Value

The matrix `N` with the basis for the null space, or an empty vector if the matrix `M` is square and of maximal rank.

### References

Venables, W. N. and Ripley, B. D. (2002) Modern Applied Statistics with S. Fourth edition. Springer.

### See Also

`qr`, `qr.Q`

### Examples

    # The function is currently defined as
    function(M)
    {
            tmp <- qr(M)
            set <- if(tmp$rank == 0) 1:ncol(M) else  - (1:tmp$rank)
            qr.Q(tmp, complete = TRUE)[, set, drop = FALSE]
    }

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