MATLAB is giving a false result to a condition that is

Hello.

I have encountered a problem while programming a little script.

The problem is I am evaluating two variables are the same within an 'if'.

Looks like MATLAB thinks they are not the same, when they obviously are, thus generating error in my program. This is what happens:

if dif == dq
    a=1
else
    a=0
end
a =

     0

When I ask matlab the values of dif and dq

>> dif

dif =

      0.0500

>> dq

dq =

      0.0500

I realised this happens when the values of dq, and dif, are generated from my program, dif is the result of the absolute value of the difference between two values of a vector, and dq is just a difference divided by two.

If I manually assign the values of dif and dq, an then evaluate dif==dq, I do get a 1.

When the program fixes the values, and even when they are the same, I evaluate dif==dq and it returns me 0.

I'm sure must be something very simple that I am not seeing, I still don't know where I'm wrong. Certainly I am new at using the MATLAB software.

Any help would be appreciated, thanks!

Answer 1

[KSSV]

You should not compare floating point numbers like that. Better, you calculate the difference and check for absolute of difference to be less then certain very small parameter. This is suggested to compare floating point numbers.

eps = 10^-6 ;   % a small parameter 
if abs(dif-dq)<=eps
    a=1
else
    a=0
end