what is the difference between manually generated data and loaded data or random data?

If we have a matrix stated as below a =

   -0.3252    0.1231   -0.1236
    0.3690   -0.3574    0.3214
    0.8524   -1.2658   -1.3698
then we would have 
EDU>> a(2,1)==0.3690

ans =

     1

But if we have a matrix which contains random numbers generated by MATLAB such as b=rand(3,3)

b =

    0.2293    0.1496    0.0159
    0.1822    0.2027    0.9575
    0.1664    0.9550    0.0257
then very suprisingly we would have 
b(2,1)==0.1822

ans =

     0

I came up to this problem while using the load data.mat command. In case I load the data it would face the same problem as randomly generated data.Can you please proide me an answer for this problem. Thank you

Answer 1

[Arnaud Miege]

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

[Maryam]

still I have

a

a =

0.1822

EDU>> areEssentiallyEqual = abs(a-0.1822) < eps(a)

areEssentiallyEqual =

0

[Arnaud Miege]

The error is with eps(a). Just use eps:

>> a = 0.1822

a =

0.1822

>> abs(a-0.1822)<eps

ans =

1

[Arnaud Miege]

You're trying to index eps with a.