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Topic: finding index of any element in a matrix
Replies: 6   Last Post: Jun 24, 2013 2:07 PM

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Nasser Abbasi

Posts: 6,253
Registered: 2/7/05
Re: finding index of any element in a matrix
Posted: Jun 24, 2013 6:33 AM
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On 6/24/2013 5:13 AM, asif khan wrote:

> eg,R = rand(3,3)
> R =
> 0.4820 0.2262 0.2518
> 0.1206 0.3846 0.2904
> 0.5895 0.5830 0.6171
> I = find(R==0.6171)
> I =
> Empty matrix: 0-by-1
> that is the problem... is there any precision problem???

Yes. You should never really use .EQ. with floating points.

In addition, what you see on the screen is not the full number
any way.

EDU>> format short
EDU>> R=rand(2)
0.8491 0.6787
0.9340 0.7577

EDU>> find(R==0.7577)
Empty matrix: 0-by-1

Error using format
0.849129305868777 0.678735154857773
0.933993247757551 0.757740130578333

To do an .EQ. on floating point (or any comparison, < or > etc..)
you should use the abs/epsilon method. This is discussed in
many places.


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