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Why can't I find the number 1.7?

2 Ansichten (letzte 30 Tage)
Chris
Chris am 14 Okt. 2013
Kommentiert: John D'Errico am 14 Okt. 2013
Why does this return an empty answer for 1.7, but not 1.6 or 1.8? I am using an older version of Matlab (2006a), I have not tried this on a newer version yet.
test=0:0.1:5000;
>> find(test==1.7);
ans = Empty matrix: 1-by-0
>> find(test==1.8);
ans = 19
>> find(test==1.6)
ans = 17
  4 Kommentare
Jan
Jan am 14 Okt. 2013
This is not an error and it does not concern Matlab only, but this happens for other languages also in exactly the same way.
John D'Errico
John D'Errico am 14 Okt. 2013
This is a problem only to the extent that you don't understand floating point numbers and how they are stored. Time to read the FAQ.

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Antworten (2)

Carla
Carla am 14 Okt. 2013
It's because your computer can't store decimal numbers in an exact form - there is always small but finite roundoff error in floating-point arithmetic. Have a look at this FAQ: http://matlab.wikia.com/wiki/FAQ
In particular, look at the section entitled "Why is 0.3 - 0.2 - 0.1 (or similar) not equal to zero?"

Yatin
Yatin am 14 Okt. 2013
Hi,
It has to do with the way floating point numbers are represented in MATLAB. May be this article helps:

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