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# Generate sequence of sine waves with changing amplitude

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Michelle Weinmann on 3 May 2021
Commented: VBBV on 4 May 2021
I'm trying to create a series of 11 sine functions with a changing amplitude. The 11 amplitudes are stored in a 1x11 array. The script is supposed to subtract two signals and generate a third. It's working until the section that assigns the signals (V1sig etc), but I just can't get the sine wave assignment correct; I keep getting errors about indexing or array sizing. I've tried a couple different ways with no success, hence why V1sig and V3sig are different. Any help would be appreciated, I'm sure I'm overlooking something simple.
f = 2.36e3;
w = 2*pi*f;
%sampling frequency
fs = 50000;
dt = 1/fs;
%Amplitude of pickup signal at each of 11 data points, and phase
Amp = [0.0654 0.0546 0.0436 0.0326 0.0219 0.0127 0.0099 0.0171 0.0272 0.0380 0.0482];
phase1 = -42*(pi/180);
%Amplitude of background signal, and phase
A2 = 0.2;
phase2 = 82*(pi/180);
%Timescale for plotting
t = 0:dt:(pi/2);
for k = 1:11
A1(k) = Amp(k);
V1(k)= A1(k)*exp(1i*(-phase1));
V2= A2*exp(1i*(-phase2));
V3(k)= V1(k)-V2;
R = real(V3);
I = imag(V3);
r = sqrt(R.^2 + I.^2);
theta(k) = atan(I/R);
V1sig = A1.*cos(w*t+phase1);
V2sig = A2*cos(w*t+phase2);
V3sig(k) = r(k).*cos(w*t+theta(k));
figure
plot(t,V1sig,t,V2sig,t,V3sig);
axis([0 pi/2 -0.5 0.5]);
legend('V1','V2','V3');
end
##### 2 CommentsShowHide 1 older comment
Michelle Weinmann on 3 May 2021
Thanks, inserted code instead of a screenshot.

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### Accepted Answer

VBBV on 3 May 2021
%f true
f = 2.36e3;
w = 2*pi*f;
%sampling frequency
fs = 50000;
dt = 1/fs;
%Amplitude of pickup signal at each of 11 data points, and phase
Amp = [0.0654 0.0546 0.0436 0.0326 0.0219 0.0127 0.0099 0.0171 0.0272 0.0380 0.0482];
phase1 = -42*(pi/180);
%Amplitude of background signal, and phase
A2 = 0.2;
phase2 = 82*(pi/180);
%Timescale for plotting
t = 0:dt:(pi/2);
for k = 1:length(Amp)
A1(k) = Amp(k);
V1(k)= A1(k)*exp(1i*(-phase1));
V2= A2*exp(1i*(-phase2));
V3(k)= V1(k)-V2;
R = real(V3(k));
I = imag(V3(k));
r = sqrt(R.^2 + I.^2);
theta(k) = atan(I/R);
V1sig(:,k) = A1(k)*cos(w*t+phase1);
V2sig(:,k) = A2*cos(w*t+phase2);
V3sig(:,k) = r*cos(w*t+theta(k));
%figure
plot(t(1:500:end),V1sig(1:500:end,k),t(1:500:end),V2sig(1:500:end,k),t(1:500:end),V3sig(1:500:end,k));
axis([0 pi/2 -0.5 0.5]);
legend('V1','V2','V3');
end
Try this
##### 1 CommentShowHide None
VBBV on 4 May 2021
%f true
f = 2.36e3;
w = 2*pi*f;
%sampling frequency
fs = 50000;
dt = 1/fs;
%Amplitude of pickup signal at each of 11 data points, and phase
Amp = [0.0654 0.0546 0.0436 0.0326 0.0219 0.0127 0.0099 0.0171 0.0272 0.0380 0.0482];
phase1 = -42*(pi/180);
%Amplitude of background signal, and phase
A2 = 0.2;
phase2 = 82*(pi/180);
%Timescale for plotting
t = 0:dt:(pi/2);
for k = 1:length(Amp)
A1(k) = Amp(k);
V1(k)= A1(k)*exp(1i*(-phase1));
V2= A2*exp(1i*(-phase2));
V3(k)= V1(k)-V2;
R = real(V3(k));
I = imag(V3(k));
r = sqrt(R.^2 + I.^2);
theta(k) = atan(I/R);
V1sig(:,k) = A1(k)*cos(w*t+phase1);
V2sig(:,k) = A2*cos(w*t+phase2);
V3sig(:,k) = r*cos(w*t+theta(k));
%figure
plot(t(1:1000:end),V1sig(1:1000:end,k),t(1:1000:end),V2sig(1:1000:end,k),t(1:1000:end),V3sig(1:1000:end,k));
axis([0 pi/2 -0.5 0.5]);
legend('V1','V2','V3');
end Sign in to comment.

### More Answers (1)

DGM on 3 May 2021
f = 2.36e3;
w = 2*pi*f;
%sampling frequency
fs = 50000;
dt = 1/fs;
%Amplitude of pickup signal at each of 11 data points, and phase
A1 = [0.0654 0.0546 0.0436 0.0326 0.0219 0.0127 0.0099 0.0171 0.0272 0.0380 0.0482]';
phase1 = -42*(pi/180);
%Amplitude of background signal, and phase
A2 = 0.2;
phase2 = 82*(pi/180);
%Timescale for plotting
t = 0:dt:(pi/2);
V1= A1*exp(1i*(-phase1));
V2= A2*exp(1i*(-phase2));
V3= V1-V2;
r = abs(V3);
theta = angle(V3);
V1sig = A1.*cos(w*t+phase1);
V2sig = A2*cos(w*t+phase2);
V3sig = r.*cos(w*t+theta);
% i'm only plotting a small section so that there's something to see
nps = 100;
for p = 1:numel(A1)
subplot(3,4,p)
plot(t(1:nps),V1sig(p,1:nps),t(1:nps),V2sig(1:nps),t(1:nps),V3sig(p,1:nps));
legend('V1','V2','V3');
end No guarantees that I didn't change anything in the edit, but I think that's the general idea. Just transpose the A vector and use implicit expansion to calculate all the signals as row vectors in an array.
##### 2 CommentsShowHide 1 older comment
DGM on 3 May 2021
They are all stored. They're just row vectors in one big array.

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