From help-request at octave dot org Sun Jan 23 20:12:56 2005
Subject: Re: Evaluating quadratic functions
From: Paul Laub <tyrosine at gmail dot com>
To: "hanrahat at comcast dot net" <hanrahat@comcast.net>
Cc: help at octave dot org
Date: Sun, 23 Jan 2005 18:16:31 -0800

Tom,

Try replacing the exponentiation operator  ^  with the element by
element exponentiation operator  .^  (dot caret).  Using ^ alone
computes a matrix power. For that a square matrix is needed. Note that
for a = [1 2; 3 4] ,  a ^ 2  and a * a give one and the same answer,
while a .^ 2 and a .* a give one and the same different answer. a must
be square for the former but not necessarily for the later.  All are
correct. Which is appropriate, though, depends on your purpose.

Paul Laub 


On Mon, 24 Jan 2005 01:50:38 +0000, hanrahat at comcast dot net
<hanrahat at comcast dot net> wrote:
> I'm having trouble understanding how to evaluate and plot quadratic functions.
> Here's a sequence that explains what I'm trying to accomplish.  In particular,
> I don't understand the error message "error: for A^b, A must be square" It doesn't
> seem that A being square has anything to do with the function.
> 
> Can anyone help me understand how to do this?
> 
> Thanks,
> 
> -- Tom
> 
> GNU Octave, version 2.1.50 (i686-pc-linux-gnu).
> Copyright (C) 1996, 1997, 1998, 1999, 2000, 2001, 2002, 2003 John W. Eaton.
> This is free software; see the source code for copying conditions.
> There is ABSOLUTELY NO WARRANTY; not even for MERCHANTIBILITY or
> FITNESS FOR A PARTICULAR PURPOSE.  For details, type `warranty'.
> 
> Please contribute if you find this software useful.
> For more information, visit http://www.octave.org/help-wanted.html
> 
> Report bugs to <bug-octave at bevo dot che dot wisc dot edu>.
> 
> octave:1> x = 1:1:2;
> octave:2> sqrt(x)
> ans =
> 
>   1.0000  1.4142
> 
> octave:3> exp(x)
> ans =
> 
>   2.7183  7.3891
> 
> octave:4> function retval = linear(x)
> > retval = x + 1;
> > endfunction
> octave:5> linear(x)
> ans =
> 
>   2  3
> 
> octave:6> function retval = quad(x)
> > retval = x^2;
> > endfunction
> octave:7> quad(x)
> error: for A^b, A must be square
> error: evaluating binary operator `^' near line 2, column 11
> error: evaluating assignment expression near line 2, column 8
> error: called from `quad'
> octave:7>
> 
> -------------------------------------------------------------
> Octave is freely available under the terms of the GNU GPL.
> 
> Octave's home on the web:  http://www.octave.org
> How to fund new projects:  http://www.octave.org/funding.html
> Subscription information:  http://www.octave.org/archive.html
> -------------------------------------------------------------
> 
>



-------------------------------------------------------------
Octave is freely available under the terms of the GNU GPL.

Octave's home on the web:  http://www.octave.org
How to fund new projects:  http://www.octave.org/funding.html
Subscription information:  http://www.octave.org/archive.html
-------------------------------------------------------------