For loop not working for me

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I'm doing some basic for loop that should return epislons for specific values and it's not working at all.
The strange thing is that when I changed the values of xx(i) and increased them it worked fine, when I checked if my conditions are found since that was the obvious mistake, I found them in the matrix of xx but the for loop doesn't assign the values as it should. Not sure what's the mistake here. Thanks a lot
clear
close all
clc
window_x=50e-6; %The window size in x direction (microns)
window_y=50e-6;
dx=2.5e-7; %The step size in x direction
dy=2.5e-7;
x_initial=-window_x/2; %The initial of the x window
y_initial=-window_y/2; %The initial of the y window
xx=x_initial:dx:-1*x_initial;
yy=y_initial:dy:-1*x_initial;
eplsn_r1 = 2.25;
eplsn_r2 = 2.1025;
lmda = 1.5e-6;
k0=2*(22/7)/lmda;
x_initial
xx
[x y]=meshgrid(xx,yy);
N=length(xx);
M=length(yy);
Eps=zeros(N,M);
iteration=0;
for i=1:N
for j=1:M
if (xx(i) ==-1.75e-6 || yy(j)==-1e-6 || xx(i)==1.75e-6 || yy(j)==1e-6)
Eps(i,j)=eplsn_r1;
iteration = iteration+1;
elseif (xx(i)==-1.5e-6 || yy(j)==-0.75e-6 || xx(i)==1.5e-6 || yy(j)==0.75e-6)
Eps(i,j)=eplsn_r2;
iteration = iteration+1;
end
end
end
iteration
I made the iteration to check if it's working and it's returning 0 on my end.

Accepted Answer

Alhussein Osama
Alhussein Osama on 15 Dec 2021
It worked now, I changed the window size to be smaller and it worked fine. It seems that there's a ratio between the size and the step size that it won't work after it.
  2 Comments
Alhussein Osama
Alhussein Osama on 15 Dec 2021
I agree with you, but I tried to use your simpler code but it didn't work though. I will try to modify it later to adjust to whay I need to do. Thanks for your help.

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More Answers (1)

Jan
Jan on 15 Dec 2021
Edited: Jan on 15 Dec 2021
xx = x_initial:dx:-1*x_initial;
if xx(i) == -1.75e-6
You cannot expect a specific value in the vector xx, because it is created by a mathematical operation with floating point values. See:
xx = 0:0.1:1
any(xx == 0.3) % FALSE!
By the way, a simpler code:
N = length(xx);
M = length(yy);
Eps = zeros(N, M);
mask1 = (abs(xx.') == 1.75e-6 | abs(yy) == 1e-6);
Eps(mask1) = eplsn_r1;
mask2 = (abs(xx.') == 1.5e-6 | abs(yy) == 0.75e-6);
Eps(mask2) = eplsn_r2;
iteration = nnz(mask1) + nnz(mask2);
For a stable code you have to consider limits. maybe:
(abs(xx.') - 1.75e-6) < 1e-8
  1 Comment
Alhussein Osama
Alhussein Osama on 15 Dec 2021
Oh, I totally forgot that since I have been away from programming for a while, thanks for your reply and your answer though.

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