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## Re: About diagonal matrices

**From**: |
Daniel J Sebald |

**Subject**: |
Re: About diagonal matrices |

**Date**: |
Sun, 01 Mar 2009 16:05:05 -0600 |

**User-agent**: |
Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.7.3) Gecko/20041020 |

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

**Re: About diagonal matrices**, *(continued)*
**Re: About diagonal matrices**, *Daniel J Sebald*, `2009/03/01`
**Re: About diagonal matrices**, *Jaroslav Hajek*, `2009/03/01`
**Re: About diagonal matrices**, *Daniel J Sebald*, `2009/03/01`
**Re: About diagonal matrices**, *Jaroslav Hajek*, `2009/03/01`
**Re: About diagonal matrices**, *Daniel J Sebald*, `2009/03/01`
**Re: About diagonal matrices**, *Jaroslav Hajek*, `2009/03/02`
**Re: About diagonal matrices**, *Daniel J Sebald*, `2009/03/02`
**Re: About diagonal matrices**, *Jaroslav Hajek*, `2009/03/02`

**Re: About diagonal matrices**, *Jaroslav Hajek*, `2009/03/01`
**Re: About diagonal matrices**, *Jaroslav Hajek*, `2009/03/01`
**Re: About diagonal matrices**,
*Daniel J Sebald* **<=**