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

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Emmanuele Mereu
Emmanuele Mereu 2017-4-12
编辑： Stephen23 2017-4-12
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.

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采纳的回答

Jan
Jan 2017-4-12

更多回答（2 个）

Santhana Raj
Santhana Raj 2017-4-12
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 2017-4-12
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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