Subscript assignment mismatch with the use of 'find'

The following as commands typed in the command window with the results:

>> X = 0:0.001:1;    
>> find(X==0.57)     

ans =

   Empty matrix: 1-by-0

>> X(571)

ans =

    0.5700

I cannot figure out why find doesn't work. I stumbled on it accidentally. This works if choose to find any other number except a special few like 0.47, 0.67, 0.41...

Answer 1

[Arturo Moncada-Torres]

I recommend you to look at this part of the MATLAB FAQ. This explains the results you are getting.

[Paulo Silva]

+1 vote for mentioning the FAQ

Answer 2

[Fangjun Jiang]

floating point comparison!!!

Answer 3

[aditya]

Thanks. But in that case...using '==' should not give a result for a lot more cases.

Also,

using linspace instead of colons for defining the vector (here, X) seems to solve the problem. I do not like the approach of comparing difference with tolerance as given in the FAQ...it is not really a good solution in my opinion.

[Walter Roberson]

Using tolerances is the only practical solution unless you have a system that has extensive interval-arithmetic operations built in. Building in that level of interval-arithmetic is hard!!