Re: About diagonal matrices

[Daniel J Sebald]

Jaroslav Hajek wrote:
> On Sun, Feb 22, 2009 at 12:49 AM, Daniel J Sebald

> > Here's a bug:
> >
> > octave:18> complex(0,Inf) - Inf
> > ans = -Inf + Infi
> > octave:23> complex(0,-Inf) + Inf
> > ans = Inf - Infi
> >
> > That should be -Inf + NaNi, I'd think.
>
>
> Why?

Eh, that looks right.  I must have gotten lost in looking at all the Inf 
scenarios.

> > Same sort of thing here:
> >
> > octave:28> complex(0,-Inf) / 0
> > warning: division by zero
> > ans = NaN - NaNi
> >
> > should be NaN - Infi.
>
>
> Not really. The reason is that the zero is converted to complex zero
> prior to the division, i.e. there is no actual complex/real operation
> implemented in Octave. An implementation using the direct algorithm
> would, of course, be superior.

OK, complex(3,4)/complex(0,0) = NaN + NaNi.  I guess it is better as is.  In 
some sense, there shouldn't be a NaN + NaNi, just NaN, otherwise there is all 
kind of implied meaning.  Same with Inf + Infi.  (Just exactly along what path 
does the limit follow?)

Alright, so:

octave:24> complex(3,0) / 0
warning: division by zero
ans = NaN - NaNi
octave:25> 3 / 0
warning: division by zero
ans = Inf

Anyone recall John Travolta when he started out in Welcome Back Kotter?  "I'm so 
confuuuuused".

Dan