IF statements to compare Imaginary Numbers

Hi,

I have been trying to work out how to use a IF statement to see if two imarinary matrixs are the same, then display "results re correct' or soething like that. My code is below

EG,

clear
clc
%-------------------Setting Up the Variables-------------------------------
X = [1,    -1]'   ;       % The Orignal Funcation
X1 = [0, -1 - 1i]' ;    % The Recieved Function

% -------------------Potential transforms matries for W -------------------
W1 = 1/(sqrt(2))*[1,1;exp(0),-exp(0)]   ;           % Transform 1
W2 = 1/(sqrt(2))*[1,1;exp(1i*pi/4),-exp(1i*pi/4)] ;  % Transform 2
W3 = 1/(sqrt(2))*[1,1;exp(1i*pi/2),-exp(1i*pi/2)] ;  % Transform 3
W4 = 1/(sqrt(2))*[1,1;exp(3i*pi/4),-exp(3i*pi/4)];   % Transform 4

%-------------------Solving to find the Value for X1-----------------------
A = W1*X   ; % solves for Transform 1 and the orignal funcation
B = W2*X   ; % solves for Transform 2 and the orignal funcation
C = W3*X  ; % solves for Transform 3 and the orignal funcation
D = W4*X  ;% solves for Transform 4 and the orignal funcation

Now the if statements that I have been working on are as follows

if A==X1
disp ('Resutls are the same')
elseif B==X1
disp ('Resutls are the same')
elseif C==X1
disp ('Resutls are the same')
elseif D==X1
disp ('Resutls are the same')
end

Now I know that the answer is D but continue to get nothing for the result. I have read about this and it has something to do with floating point numbers and what Matlabs can display. I am a little lost as to how the code should look so that the answer D will display something saying it is the same.

Any help would be appriciated

Thanks Kayne

Answer 1

[Paulo Silva]

Do this

D==X1

ans=
1
0

It's really something about floating point, try doing this:

(D>=X1-eps & D<=X1+eps)

now replace all the comparisons on your code the same way and all should work.

Better explanation and ways to deal with the situation can be found here

[Kayne]

Thanks for the reply Paulo,

Your solution worked and has helped me greatly. Now to get into the finner details and understand why it worked.

Thanks heaps for your time and help

Kind Regards,

Kayne

[Paulo Silva]

Do this: X1-D , it isn't zero but very close to it, very near eps.

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