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## rank(gf) doesn't really work?

 From: Lapo Luchini Subject: rank(gf) doesn't really work? Date: Tue, 11 Oct 2005 11:13:30 +0000 (UTC) User-agent: Loom/3.14 (http://gmane.org/)

```Maybe I'm missing some important point (e.g. "gfrank" is not defined) and this
is really not supported, but it gives different result on gf() than on a normal
array so just maybe it shuold work..?

\$ B=gf([0,1,0,0,1,1;
0,0,1,1,1,0;
0,1,1,1,0,0;
1,0,1,1,0,0;
1,1,0,1,0,0;
1,1,1,0,0,0]);
\$ D=gf([0,1,0,0,1,1;
0,0,1,1,1,0;
0,1,1,1,0,0;
1,0,1,1,0,0;
1,1,0,1,0,0;
0,1,1,0,0,0]);
\$ B+D
ans =
GF(2) array.

Array elements =

0  0  0  0  0  0
0  0  0  0  0  0
0  0  0  0  0  0
0  0  0  0  0  0
0  0  0  0  0  0
1  0  0  0  0  0
\$ rank(B)
ans = 6
\$ rank(D)
ans = 4

Then, if B is full-rank (6 out of 6) how can possibly D be rank 4 if the first 5
lines are the very same 5 lines that in B were linearly independent?

It just seems that it works, but only on square matrices, and it just ignores
any other column:
\$ rank(B(1:5,1:5))
ans = 4
\$ rank(B(1:5,2:6))
ans = 5
\$ rank(B(1:5,:))
ans = 4

I would expect last line to be 5 as well. Maybe rank(B(1:5,:)) just uses the
first 5 columns in the 5x6 matrix?

Mhh...?

Lapo

--
Lapo Luchini
www.lapo.it (ICQ UIN: 529796)

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