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clear

K = 1;

M = zeros(1,1000);

for omega = 1:1000

s = omega*i;

G = K/(s*(s+1.71)*(s+100));

M(omega) = G;

end

omega = 1:1000;

phase = rad2deg(angle(M));

dB = 20*log10(abs(M));

semilogx(omega,dB)

title('Semilogarithmic Decibel Plot for K = 1')

xlabel('Frequency Range (rad/s)')

ylabel('Decibels (dB)')

grid on

I am trying to create two plots using loop programming (for…end), one plot is the magnitude

20 log M (this is called decibel dB) for from 0.1 to 1000 , and the other plot is the phase (in degree) for from 0. 1 to 1000.

I have attached the code for 1-1000 but when i chnage the 1 value i get an error saying only integers can be used. Can anyone help me fix to this shows a graph for the boundary 0.1-1000.

Jakob B. Nielsen
on 16 Mar 2020

Your issue is that if you make a for loop for 0.1 to 1000, and then use that same counter as an index, when you then type M(omega) = G; you try to place into the 0.1'th index of M, the result G. Clearly, this is impossible.

Separate your loop counter from your X, like this. This also means you can make any change you want just to your omega input, and the remainder of the script will still fly.

clear

K = 1;

omega = 0.1:0.1:1000; %omega goes from 0.1, in steps of 0.1, to 1000.

M = zeros(1,size(omega,2)); %adjust your preallocation size to be equal to your omega length

for count= 1:size(omega,2) %and the loop counter as well

s = omega(count)*i; %finally, take the loop counter index of omega

G = K/(s*(s+1.71)*(s+100));

M(count) = G;

end

phase = rad2deg(angle(M));

dB = 20*log10(abs(M));

semilogx(omega,dB)

title('Semilogarithmic Decibel Plot for K = 1')

xlabel('Frequency Range (rad/s)')

ylabel('Decibels (dB)')

grid on

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