lm having a problem with code for dispersion when ever l try to run, it say the variable 'dispersion' in line 20 is changing the size of every loop so how do l solve this

clc;

clear all;

close all;

format long;

wl=1:0.05:2;

wl1=wl*1e-6;

vc=299792458;

w=2*pi*(vc./wl1);

Wavelength=wl*1e-6;

Fresult={'ofc_y.txt', 'ofc_x.txt'};

for i=1:2

[neff,beta,alpha,alphadB]=textscan(Fresult{i},....

'%f %f %f %f');

beta(i,:)=beta;

alpha(i,:)=alpha;

alphadB(i,:)=alphadB;

b1=diff(beta(i,:))./diff(w);

Dispersion(i,:)=((diff(b1)./diff(wl1(1:end-1))));

end

figure(1)

plot(wl1*1e6,neffr(1,:),'-r',wl1*1e6,neffr(2,:),'-b');

legend('y-mode','x-mode','Location','best');

xlabel('Wavelenght(\mu m)');

ylabel('Effective Index');

title('Effective Index vs wavelength');

figure(2)

plot(wl1*1e6,betar(1,:),'-r',wl1*1e6,betar(2,:),'k');

legend('y-mode','x-mode','Location','best');

xlabel('Wavelenght(\mu m)');

ylabel('beta');

title('beta vs wavelength');

figure(3)

plot(wl*1e6,alphadBr(1,:),'-r',wl*1e6,alphadBr(2,:),'k');

legend('y-mode','x-mode','Location','best');

xlabel('Wavelenght(\mu m)');

ylabel('alphadB');

title('alphadB vs wavelength');

figure(4)

plot(wl1(1:end-2)*1e6,Dispersion(1,:),'-r',wl1(1:end-2)*1e6,Dispersion(2,:),'k');

legend('y-mode','x-mode','Location','best');

xlabel('Wavelenght(\mu m)');

ylabel('Dispersion');

title('Dispersion vs wavelength');

Answer 1

[Abderrahim. B]

Hi!

I beleive that s only a warning, to avoid it preallocate for Disperssion variable.

Demo:

Without preallocation :

A = randi(10,20,20) ;
for ii = 1:20
    B(ii, :) = A(ii, :) ;
   
end
B

B = 20×20

10 1 9 9 5 1 7 4 1 4 1 2 7 5 7 8 3 4 5 10 5 2 3 5 4 9 9 8 10 9 8 4 3 2 9 8 2 1 7 4 2 5 6 3 3 5 2 9 7 2 10 9 6 8 2 9 1 4 6 7 8 3 10 8 7 8 5 2 3 9 6 7 7 1 2 9 8 6 3 10 3 1 7 3 4 3 1 5 9 10 6 7 6 1 5 6 1 9 10 5 10 8 7 10 1 8 9 7 4 8 8 3 1 8 1 9 8 1 10 2 10 3 8 8 6 4 2 7 2 9 3 8 1 9 7 4 5 7 6 2 8 7 5 3 10 2 1 4 9 8 1 3 4 4 3 7 9 9 3 6 8 1 4 3 3 3 1 7 5 2 3 1 8 8 2 10 2 4 2 5 1 4 2 4 1 9 4 10 8 3 7 9 1 7 7 10 1 2 6 7

With preallocation:

B = zeros(size(A)) ; % preallocation for B using function zeros
for ii = 1:20
    B(ii, :) = A(ii, :) ;
   
end
B

B = 20×20

10 1 9 9 5 1 7 4 1 4 1 2 7 5 7 8 3 4 5 10 5 2 3 5 4 9 9 8 10 9 8 4 3 2 9 8 2 1 7 4 2 5 6 3 3 5 2 9 7 2 10 9 6 8 2 9 1 4 6 7 8 3 10 8 7 8 5 2 3 9 6 7 7 1 2 9 8 6 3 10 3 1 7 3 4 3 1 5 9 10 6 7 6 1 5 6 1 9 10 5 10 8 7 10 1 8 9 7 4 8 8 3 1 8 1 9 8 1 10 2 10 3 8 8 6 4 2 7 2 9 3 8 1 9 7 4 5 7 6 2 8 7 5 3 10 2 1 4 9 8 1 3 4 4 3 7 9 9 3 6 8 1 4 3 3 3 1 7 5 2 3 1 8 8 2 10 2 4 2 5 1 4 2 4 1 9 4 10 8 3 7 9 1 7 7 10 1 2 6 7

Hope this helps