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From: Aino on 10 Aug 2010 10:07
Here a simple, annoying problem:

qmax=6;
Q=[-qmax:2:-2,-1:0.4:1,2:2:qmax]'

Q =

-6.000000000000000
-4.000000000000000
-2.000000000000000
-1.000000000000000
-0.600000000000000
-0.200000000000000
0.200000000000000
0.600000000000000
1.000000000000000
2.000000000000000
4.000000000000000
6.000000000000000

>> q=-4
q =
-4

>> find(Q==q)
ans =
2

*Works!

>> q=0.2
q =
0.200000000000000

>> find(Q==q)
ans =
Empty matrix: 0-by-1

*Doesn't work..

>> whos
Name Size Bytes Class Attributes

Q 12x1 96 double
ans 0x1 0 double
q 1x1 8 double
qmax 1x1 8 double

Why does find not find?

-Aino
From: dpb on 10 Aug 2010 10:07
Aino wrote:
> Here a simple, annoying problem:
....
[example of floating point elided for brevity]
....
> Why does find not find?

See the ML FAQ at

<http://matlabwiki.mathworks.com/MATLAB_FAQ#Why_is_0.3-0.2-0.1_not_equal_to_zero_.28or_similar.29.3F>


--
From: Sean on 10 Aug 2010 10:13
"Aino" <aino.tietavainen(a)removeThis.helsinki.fi> wrote in message <i3rme9$12$1(a)fred.mathworks.com>...
> Here a simple, annoying problem:
>
> qmax=6;
> Q=[-qmax:2:-2,-1:0.4:1,2:2:qmax]'
>
> Q =
>
> -6.000000000000000
> -4.000000000000000
> -2.000000000000000
> -1.000000000000000
> -0.600000000000000
> -0.200000000000000
> 0.200000000000000
> 0.600000000000000
> 1.000000000000000
> 2.000000000000000
> 4.000000000000000
> 6.000000000000000
>
> >> q=-4
> q =
> -4
>
> >> find(Q==q)
> ans =
> 2
>
> *Works!
>
> >> q=0.2
> q =
> 0.200000000000000
>
> >> find(Q==q)
> ans =
> Empty matrix: 0-by-1
>
> *Doesn't work..
>
> >> whos
> Name Size Bytes Class Attributes
>
> Q 12x1 96 double
> ans 0x1 0 double
> q 1x1 8 double
> qmax 1x1 8 double
>
> Why does find not find?
>
> -Aino

Question 6.1
http://matlabwiki.mathworks.com/MATLAB_FAQ
From: Aino on 10 Aug 2010 10:54
"Sean " <sean.dewolski(a)nospamplease.umit.maine.edu> wrote in message <i3rmpg$m4m$1(a)fred.mathworks.com>...
> "Aino" <aino.tietavainen(a)removeThis.helsinki.fi> wrote in message <i3rme9$12$1(a)fred.mathworks.com>...
> > Here a simple, annoying problem:
> >
> > qmax=6;
> > Q=[-qmax:2:-2,-1:0.4:1,2:2:qmax]'
> >
> > Q =
> >
> > -6.000000000000000
> > -4.000000000000000
> > -2.000000000000000
> > -1.000000000000000
> > -0.600000000000000
> > -0.200000000000000
> > 0.200000000000000
> > 0.600000000000000
> > 1.000000000000000
> > 2.000000000000000
> > 4.000000000000000
> > 6.000000000000000
> >
> > >> q=-4
> > q =
> > -4
> >
> > >> find(Q==q)
> > ans =
> > 2
> >
> > *Works!
> >
> > >> q=0.2
> > q =
> > 0.200000000000000
> >
> > >> find(Q==q)
> > ans =
> > Empty matrix: 0-by-1
> >
> > *Doesn't work..
> >
> > >> whos
> > Name Size Bytes Class Attributes
> >
> > Q 12x1 96 double
> > ans 0x1 0 double
> > q 1x1 8 double
> > qmax 1x1 8 double
> >
> > Why does find not find?
> >
> > -Aino
>
> Question 6.1
> http://matlabwiki.mathworks.com/MATLAB_FAQ

Hi,

and so it is, that find(abs(Q-q) < 10^(-5)) works. :)

Thank you,
Aino
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