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Subscript assignment mismatch with the use of 'find'

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aditya
aditya 2011년 8월 31일
마감: MATLAB Answer Bot 2021년 8월 20일
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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답변 (3개)

Arturo Moncada-Torres
Arturo Moncada-Torres 2011년 8월 31일
I recommend you to look at this part of the MATLAB FAQ. This explains the results you are getting.
  댓글 수: 1
Paulo Silva
Paulo Silva 2011년 8월 31일
+1 vote for mentioning the FAQ
Fangjun Jiang
Fangjun Jiang 2011년 8월 31일
floating point comparison!!!
aditya
aditya 2011년 8월 31일
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.
  댓글 수: 1
Walter Roberson
Walter Roberson 2011년 9월 2일
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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