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Using Help using filter function in Matlab

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Telema Harry
Telema Harry on 27 Nov 2020
Edited: Telema Harry on 29 Nov 2020
clear all
G = @(u,t)(25-(5-(u)).^2);
u = 0;
%g0 = G(0.1,0);
phase = 0;
% Extremum Seeking Control Parameters
freq = 10*2*pi; % sample frequency
dt = 1/freq;
T = 10; % total period of simulation (in seconds)
A = .2; % amplitude
omega = 10*2*pi; % 10 Hz
phase = 0;
K = 5; % integration gain
%*****************************************************************
% Design of High Pass filter. the cut of frequency is 0.2
%a and b at the output variable from the butter function
b_order = 1; % The butterworth filter order
butter_freq = 1;
[b,a] = butter(b_order,butter_freq * 2 * dt, 'high');
%freqz(b,a)
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%Intial condition
%ys = zeros(1,b_order+1);
uhat(1) = u(1);
for i = 1 : T/dt
t = (i-1)*dt;
yvals(i) = G(u,t);% This variable stores the values of G at every interation
ys(i) = yvals(i);
HPFnew = filter(b,a,ys(i)); % This is the value of the output signal after passing through the filter.
HPFnew_vals(i) = HPFnew;
xi = HPFnew.*sin(omega.*t + phase);
uhat = uhat + xi.*K.*dt;
u = uhat + A*sin(omega*t + phase);
uhats(i) = uhat;
uvals(i) = u;
end
t = dt:dt:T;
figure
plot(t, HPFnew_vals)
%figure
%fplot(@(u) (25-(5-(u)).^2),[0 T]) % Ploting the original function.
% The next step is to multiply the output cost function G with the filter
% I will call that variable rho
t = dt:dt:T;
% Plot of U against Time
figure
subplot(2,1,1)
%ax1 = nexttile;
%plot([1:length(uhat)],uhat,'r','lineWidth',1)
plot(t,uhats,'r','lineWidth',1)
hold on
%plot([1:i],uvals,'k','lineWidth',1)
plot(t,uvals,'k','lineWidth',1)
hold off
xlabel ('Time')
ylabel('U')
legend('Uhat','U')
grid on
subplot(2,1,2)
%ax2 = nexttile;
%plot([1:length(yvals)],yvals,'r','lineWidth',1)
plot(t,yvals,'b','lineWidth',1)
xlabel ('Time')
ylabel('G')
grid on
I am trying to pass my output signal yvals(i) = G(u,t) through a butter highpass filter. The code runs but my results is totally different from what I was expecting.
This is the result obtained.
Result Obtained
This is the result expected. I don't know what i'm doing wrong?
  3 Comments
Telema Harry
Telema Harry on 27 Nov 2020
I am trying to figure out why the results from my code is different.

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Accepted Answer

VBBV
VBBV on 27 Nov 2020
Edited: VBBV on 27 Nov 2020
%true
xi = HPFnew.*sin((omega.*t+phase)*pi/180)
u = uhat +A*sin((omega*t+phase)*pi/180)
Try the above. Also see the filter function conditions

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