From help-octave-request at bevo dot che dot wisc dot edu Fri Apr  2 06:11:39 2004
Subject: Re: Zero entries in one column of a matrix
From: Paul Kienzle <pkienzle at users dot sourceforge dot net>
To: "Henry F. Mollet" <mollet at pacbell dot net>
Cc: Octave_post Help <help-octave at bevo dot che dot wisc dot edu>
Date: Fri, 2 Apr 2004 07:09:55 -0500

t1 = M(:,2) selects column 2
t2 = t1 ~= 0 turns the column into an index
t3 = M(t2,2) uses the boolean index t2 to select rows from column 2 of M

M(M(:,2) ~= 0,2) does all the above, including creating t1,t2,t3,
but not assigning names to them.

Paul Kienzle
pkienzle at users dot sf dot net

On Thu, Apr 01, 2004 at 10:02:57AM -0800, Henry F. Mollet wrote:
> Thanks for clear explanation.
>
> Can I now also look at it as follows?
> In M (: , 2) the ":" operator? says use all entries/rows in the second
> column of M;
> whereas in M (M(:,2) ~= 0 , 2), the implied ":" operator? looks at the
> statement row by row and when it sees a boolean false (=0) says this is
> *not* an index and therefore the entry (which was an actual 0) has to 
> be
> skipped?
> Henry



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