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Re: Dot product (nx1).*(nxm)
From: |
Mike Miller |
Subject: |
Re: Dot product (nx1).*(nxm) |
Date: |
Mon, 6 Dec 1999 11:27:26 -0600 (CST) |
On Mon, 6 Dec 1999, Joao Cardoso wrote:
> ah, yes, now I understand it. But your explanation skips an important step:
> you was speaking of matrix A, and suddenly starts speaking of column vector p
> :-)
> My problem was (is!) that the notation p(:,[1 1 1]) is applied to matrices,
> and if p is a column vector, how can one specify its columns?
Column vector p is a 1xn matrix. So the logic is exactly the same as for
mxn matrix A, except that m=1. If size(A) = [10 3], and I specify
A(:,[2 5]), I will get an error message because there are not 5 columns in
A. The same holds for p(:,[1 2 3]) because there is only one column in p,
and there is no column 2 and no column 3. So, for column vectors, one
must not specify a column value greater than one. Things of this form are
fine: p(:,ones(1,m)) where m is any positive integer.
> > Does that clarify the meaning of line 5 above?
>
> yes, thanks. But the notation is not self-evident, as I said.
But it is sensible, don't you think? I can't think of a better way.
> > So far so good, but in MATLAB you can get those elements out of the matrix
> > and into a column vector using this command:
> >
> > A(find(A<.5))
> >
> > That doesn't work in Octave. Is there some other way that Octave can
> > extract those numbers from the matrix? Is it as efficient?
>
> As John Eaton said, use do_fortran_indexing=1 for this case.
Yes. I was a little embarrassed that I forgot that one. I'm much more
experienced with MATLAB than I am with Octave and I sometimes forget the
Octave-specific features.
Thanks, Joao, for all of your contributions to Octave and to this list!
Regards,
Mike
--
Michael B. Miller
University of Missouri--Columbia
http://taxa.psyc.missouri.edu/~mbmiller/
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-----------------------------------------------------------------------
- Dot product (nx1).*(nxm), Andre Bonfrer, 1999/12/04
- RE: Dot product (nx1).*(nxm), Heber Farnsworth, 1999/12/04
- RE: Dot product (nx1).*(nxm), Mike Miller, 1999/12/04
- Re: Dot product (nx1).*(nxm), Joao Cardoso, 1999/12/05
- Re: Dot product (nx1).*(nxm), Joao Cardoso, 1999/12/05
- Re: Dot product (nx1).*(nxm), Mike Miller, 1999/12/06
- Re: Dot product (nx1).*(nxm), John W. Eaton, 1999/12/06
- Re: Dot product (nx1).*(nxm), Joao Cardoso, 1999/12/06
- Re: Dot product (nx1).*(nxm),
Mike Miller <=
- speed issues (was Re: Dot product (nx1).*(nxm)), Mike Miller, 1999/12/06
- Re: Dot product (nx1).*(nxm), Dr Andre Bonfrer, 1999/12/05