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Why does "find" command fail to find a number in this vector?

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Emmanuele Mereu
Emmanuele Mereu am 12 Apr. 2017
Bearbeitet: Stephen23 am 12 Apr. 2017
Hello everybody, I use MATLAB as a beginner and I would like to understand why the "find" command does not work in this particular case.
I must know the position occupied by the number 0.24 in this vector:
v=0.01:0.01:4;
In the variable editor I see that 0.2400 is stored in row 1, column 24, so I wrote this instruction:
pointer=find(v==0.24)
in the workspace without ";" so that i can see the output, but instead of "pointer=24" as I expected this message appeared:
"pointer = 1×0 empty double row vector"
How is that possible?
Also, if I search other numbers it happens that "find" can determine the position of, for example, 0.25 but it returns the same message of empty vector searching 0.29.
Thaks.
  2 Kommentare
Emmanuele Mereu
Emmanuele Mereu am 12 Apr. 2017
Bearbeitet: Stephen23 am 12 Apr. 2017
Using fprintf('%.30f\n',v(24)) as you suggested in the first link I realized the problem. Tank you again for the quick answer.

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Jan
Jan am 12 Apr. 2017

Weitere Antworten (2)

Santhana Raj
Santhana Raj am 12 Apr. 2017
The issue is with representation of floating point numbers. Since the variable 'v' is double, it cannot exactly represent/store 0.024. Hence you cannot compare for exact value. Instead you can try this:
find((v<=0.245) & (v>=0.239))
Hope this helps.

Thorsten
Thorsten am 12 Apr. 2017
You can use
find(round(100*v) == 24)
The reason that the straight-forward approach does not work is the representation of floating point numbers, as already mentioned above.

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