issues with function find()

I am using find() to find the index of a number in a matrix, but it is returning an empty matrix yet am sure that the number is part of that matrix. Here is the code

tr=0:.1:20;
b=find(tr==2.4)

and it is returning

b =
   Empty matrix: 1-by-0

Please I need your help. What am I doing wrong or what should I do instead?

Answer 1

[Azzi Abdelmalek]

Try this

tr=0:.1:20;
b=find(tr==0.1*24)

Answer 2

[Brian B]

Try

tr=0:.1:20;
tr = round(tr*1e12)/1e12;
b=find(tr==2.4)

This is a problem with finite precision. See the explanation offered at http://matlab.wikia.com/wiki/FAQ#Why_is_0.3_-_0.2_-_0.1_.28or_similar.29_not_equal_to_zero.3F.

[Brian B]

Actually, if you're using non-integer numbers, a better method is

 b= find(abs(tr - 2.4)<1e-12)