The find function does not find the attribute element and outputs an empty row vector. What's the reason?

Here's my code.

for example,

V_bg=0.6:1/100:1.2;

output=find(V_bg==0.9);

i want to find value 0.9 but the ans is just 1x0 empty double row vector ?

i don't why

[Stephen23]

"What's the reason?"

Because you are testing for exact equivalence of values which are not exactly the same.

Read more about binary floating point numbers:

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

https://www.mathworks.com/matlabcentral/answers/316889-why-two-equal-numbers-are-not-equal

http://www.mathworks.com/matlabcentral/answers/102419-how-do-i-determine-if-the-error-in-my-answer-is-the-result-of-round-off-error-or-a-bug

http://www.mathworks.com/matlabcentral/answers/140656-about-numerical-difficulty-of-equality-comparison-operation-between-two-double-real-numbers-in-matlab

This is worth reading as well:

https://docs.oracle.com/cd/E19957-01/806-3568/ncg_goldberg.html

http://faculty.tarleton.edu/agapie/documents/cs_343_arch/papers/1991_Goldberg_FloatingPoint.pdf

Answer 1

[Asmit Singh]

To find a noninteger value using the find function, it is recommended to use a tolerance value based on your data. Otherwise, the result is sometimes an empty matrix due to floating-point roundoff error. You can have look at the documentation for further details.

V_bg=0.6:1/100:1.2;
% change the tolerance level according to your liking
output=find(abs(V_bg-0.9)<0.001);

[sangjun han]

good answer!!.