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

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.

[Stephen23]

Read about some of the side effects of floating-point numbers:

https://www.mathworks.com/matlabcentral/answers/321709-strange-behaviour-of-matlab-find-command

https://www.mathworks.com/matlabcentral/answers/320473-we-found-a-possible-bug-in-our-matlab

[Emmanuele Mereu]

Using fprintf('%.30f\n',v(24)) as you suggested in the first link I realized the problem. Tank you again for the quick answer.

Answer 1

[Jan]

:-) The evergreen frequently asked question. See.

https://www.mathworks.com/matlabcentral/answers/57444-faq-why-is-0-3-0-2-0-1-not-equal-to-zero

Answer 2

[Santhana Raj]

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.

Answer 3

[Thorsten]

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.