# range

range (span) of A^k

## Calling Sequence

    [X,dim]=range(A,k)

## Arguments

A

  real square matrix

k

  integer

X

  orthonormal real matrix

dim

  integer (dimension of subspace)

## Description

Computation of Range `A^k` ; the first dim rows of `X` span the range of `A^k`. The last rows of `X` span the orthogonal complement of the range. `X*X'` is the Identity matrix

## Examples

    A=rand(4,2)*rand(2,4);   // 4 column vectors, 2 independent.
    [X,dim]=range(A,1);dim   // compute the range

    y1=A*rand(4,1);          //a vector which is in the range of A
    y2=rand(4,1);            //a vector which is not  in the range of A
    norm(X(dim+1:$,:)*y1)    //the last entries are zeros, y1 is in the range of A
    norm(X(dim+1:$,:)*y2)    //the last entries are not zeros

    I=X(1:dim,:)'            //I is a basis of the range
    coeffs=X(1:dim,:)*y1     // components of y1 relative to the I basis

    norm(I*coeffs-y1)        //check

## See Also

- fullrfk
- rowcomp

## Used Functions

The `range` function is based on the rowcomp function which uses the svd decomposition.