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From: Mayi DA on 17 Jul 2010 09:08
Dear all
As you know, 1*[] get [], and 1*NaN can get NaN.
Let's see what will gain when Nan*[]? The answer that MATLAB gives is [].
Can anyone give me an explanation?

best regard
mayi
2010-07-17
From: Matt J on 17 Jul 2010 09:25
"Mayi DA" <damayi(a)gmail.com> wrote in message <i1s9vj$mn3$1(a)fred.mathworks.com>...
> Dear all
> As you know, 1*[] get [], and 1*NaN can get NaN.
> Let's see what will gain when Nan*[]? The answer that MATLAB gives is [].
> Can anyone give me an explanation?
============

All operations with [] give [] because you can't make something from nothing. Why do you think the result should be different?



>> []+1

ans =

[]

>> []+[]

ans =

[]

>> []/[]

ans =

[]

>> []*[]

ans =

[]
From: Mayi DA on 17 Jul 2010 10:41
nan*[] , why not result as nan?
ans =

NaN

>> nan/nan

ans =

NaN

>> nan+1

ans =

NaN

>> nan*1

ans =

NaN

"Matt J " <mattjacREMOVE(a)THISieee.spam> wrote in message <i1savh$njf$1(a)fred.mathworks.com>...
> "Mayi DA" <damayi(a)gmail.com> wrote in message <i1s9vj$mn3$1(a)fred.mathworks.com>...
> > Dear all
> > As you know, 1*[] get [], and 1*NaN can get NaN.
> > Let's see what will gain when Nan*[]? The answer that MATLAB gives is [].
> > Can anyone give me an explanation?
> ============
>
> All operations with [] give [] because you can't make something from nothing. Why do you think the result should be different?
>
>
>
> >> []+1
>
> ans =
>
> []
>
> >> []+[]
>
> ans =
>
> []
>
> >> []/[]
>
> ans =
>
> []
>
> >> []*[]
>
> ans =
>
> []
From: dpb on 17 Jul 2010 10:46
Mayi DA wrote:
> nan*[] , why not result as nan? ans =
>
....examples of operations (none including [] ) elided for brevity...

As noted, none of those examples include [] so to make your proposed
operation do so would definitely create non-orthogonal behavior in
Matlab _a_very_bad_thing_ (tm)....

But, just for argument, what purpose would it serve that can't be
accomplished otherwise more consistently?

--
From: Jan Simon on 17 Jul 2010 12:38
Dear Mayi,

> As you know, 1*[] get [], and 1*NaN can get NaN.
> Let's see what will gain when Nan*[]?

Although "NaN" means "not a number" it is a scalar DOUBLE and therefore a number. In consequence, the dimensions of "1 * []" and "NaN * []" must be equal and the multiplication must be associative (considering the limited floating point precision):
1 * NaN * [] == (1 * NaN) * [] == 1 * (NaN * [])

I'm not really convinced that "1 / []" is an error, because "Matrix dimensions must agree", while "[] / 1" is calculated to be [] without the need for agreeing dimensions.

Kind regards, Jan
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