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Subscript assignment mismatch with the use of 'find'

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aditya
aditya le 31 Août 2011
Clôturé : MATLAB Answer Bot le 20 Août 2021
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...

Réponses (3)

Arturo Moncada-Torres
Arturo Moncada-Torres le 31 Août 2011
I recommend you to look at this part of the MATLAB FAQ. This explains the results you are getting.
  1 commentaire
Paulo Silva
Paulo Silva le 31 Août 2011
+1 vote for mentioning the FAQ

Fangjun Jiang
Fangjun Jiang le 31 Août 2011
floating point comparison!!!

aditya
aditya le 31 Août 2011
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 commentaire
Walter Roberson
Walter Roberson le 2 Sep 2011
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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