Logical indexing in maltab

Hello,

I need help regarding a code.:

Sal = para(i,7); y= X(X<Sal); this doesn't change the output

The vaulue of Sal is = 0.005. If I use this, then it returns the right value.

y = X(X<0.005); this returns the correct output.

How do I resolve this issue.

Thanks.

[Stephen23]

Learn about binary floating point numbers, and how they cannot accurately represent all decimal fractions:

http://de.mathworks.com/matlabcentral/answers/57444-faq-why-is-0-3-0-2-0-1-not-equal-to-zero

You might also like to try using this, to find out what the value really is:

http://de.mathworks.com/matlabcentral/fileexchange/22239-num2strexact--exact-version-of-num2str-

Answer 1

[James Tursa]

If I understand your question, you are saying that y= X(X<Sal) returns a different result than y = X(X<0.005), even though Sal = 0.005.

I would hazard a guess that Sal is not really 0.005, but is a number close to 0.005 that displays the same as 0.005. What do you get with the following:

Sal == 0.005

[Bharat]

Hi James,

Yes y is the same as X when I use y = X(X<Sal).

Sal = 0.005010368459505, (higher than 0.005 and hence the result shouldn't change )

[Bharat]

I just checked. y=X(X<0.005010368459505) also doens't work. however y=X(X<0.005) works, which suggests that it related to number of significant digits. How do I change the number of significant digits?

Thanks

[James Tursa]

I think you now need to give us a more complete picture of what you are doing and what "doesn't work" means. If y=X(X<0.005) "works", then why aren't you doing that explicitly? Is the real problem that you need to round Sal to the nearest 3-decimal place number for some reason? Or what?

Answer 2

[Walter Roberson]

http://matlab.wikia.com/wiki/FAQ#Why_is_0.3_-_0.2_-_0.1_.28or_similar.29_not_equal_to_zero.3F