why eq says they are not equal

I have two equal vectors a = b. When I check for equality:

y = eq(a, b)
find(y==0)

I get most of values, meaning they are NOT equal.

What would be the reason for this?

N.

[Jan]

What does the "find(a==0)" do in your code?

[Nuchto]

Sorry, it was wrong put, "a" should be the output of eq(a,b).

[Jan]

Then please edit the question instead of adding this important information as a comment.

[Nuchto]

Thanks, I did.

[Jan]

@Nuchto: Is your problem solved?

Answer 1

[Muruganandham Subramanian]

Hi Nuchto,

Check this below link:

http://www.mathworks.in/help/techdoc/ref/eq.html

[Nuchto]

I have checked the help, but it didn't answer to my question.

Answer 2

[Jan]

To compare two vectors use:

r = isequal(a, b)

or to find the difference between vectors (or other arrays) of the same size:

any(a - b)

Note, that the later replies FALSE even for ones(1,10) and ones(1,1).

If you only assume, that the vectors have equal values, check a - b and note, that the limited precision of the type double leads to effects like:

03. - 0.2 ~= 0.1

Then check "almost equal" by:

limit = eps(max(max(abs(a(:)), abs(b(:)))));
% or:   eps(max(abs(a(:)), abs(b(:))));
% or:   the same times 10
a_eq_b = isequal(size(a), size(b)) & all(abs(a - b) < limit);

The choise of the limit depends on the physical meaning of the variables. There is no unique definition to distinguish measurement noise from noise caused by numerical artifacts for a tiny values.

Answer 3

[Walter Roberson]

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