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Subscript assignment mismatch with the use of 'find'

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aditya
aditya 2011-8-31
关闭： MATLAB Answer Bot 2021-8-20
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...

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回答（3 个）

Arturo Moncada-Torres
I recommend you to look at this part of the MATLAB FAQ. This explains the results you are getting.
Fangjun Jiang
Fangjun Jiang 2011-8-31
floating point comparison!!!
aditya
aditya 2011-8-31
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.
  1 个评论
Walter Roberson
Walter Roberson 2011-9-2
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!!

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