colcomp column compression, kernel, nullspace

## Syntax

    [W,rk]=colcomp(A [,flag] [,tol])

## Arguments

A

  real or complex matrix

flag

  character string

tol

  real number

W

  square non-singular matrix (change of basis)

rk

  integer (rank of `A`)

## Description

Column compression of `A`: `Ac = A*W` is column compressed i.e

`Ac=[0,Af]` with `Af` full column rank, rank(`Af`) = rank(`A`) = `rk`.

`flag` and `tol` are optional parameters: `flag = 'qr'` or `'svd'` (default is `'svd'`).

`tol` = tolerance parameter (of order `%eps` as default value).

The `ma-rk` first columns of `W` span the kernel of `A` when `size(A)=(na,ma)`

## Examples

    A=rand(5,2)*rand(2,5);
    [X,r]=colcomp(A);
    norm(A*X(:,1:$-r),1)

## See also

- rowcomp
- fullrf
- fullrfk
- kernel