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Re: Novice question on A \ b


From: Geordie McBain
Subject: Re: Novice question on A \ b
Date: Fri, 11 Mar 2005 12:05:41 +1100
User-agent: Mutt/1.5.6+20040907i

On Thu, Mar 10, 2005 at 04:41:10PM -0800, John B. Thoo wrote:
> Hi.  According to the Octave manual, when using  A \ b,  if the 
> coefficient matrix is singular, Octave will print a warning message and 
> compute a minimum norm solution.
> 
> This is what I tried.
> 
> 
> octave:18> A = [ [1, 1, 2, 3]' [0, 0, 4, 4]']; b = [3, 0, -1, 0]'; A \ b
> ans =
> 
>    1.40000
>   -1.00000
> 
> 
> I think this is the minimum norm solution, but Octave did not issue a 
> warning.  What is wrong with my thinking?

I think Octave only warns when a square matrix is (numerically)
singular.  Since no nonsquare matrices are nonsingular, it could
reasonably be argued that the warning would be redundant.

Geordie McBain
www.aeromech.usyd.edu.au/~mcbain



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