spanplus(1)

NAME
spanplus - sum of subspaces

CALLING SEQUENCE
[X,dim,dima]=spanplus(A,B[,tol])

PARAMETERS

A, B
    : two real or complex matrices with equal number of rows

X   : orthogonal or unitary square matrix

dim, dima
    : integers, dimension of subspaces

tol : nonnegative real number

DESCRIPTION
computes a  basis X such that:

the first dima columns of X span Range(A)
and the following (dim-dima) columns make a basis of A+B
relative to A.

The dim first columns of X make a basis for A+B.

One has the following canonical form for [A,B]:
         [*,*]    (dima rows)
X'*[A,B]=[0,*]    (dim-dima rows)
         [0,0]

tol is an optional argument (see function code).

SEE ALSO
spaninter, im_inv, spantwo

AUTHOR
F. D.