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skooteryup
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Hey guys, I'm working on a MATLAB program to find Fourier coefficients.
The problem with it: [STRIKE]it gives a graph that has a different period and amplitude than the original function (although its the same general shape).[/STRIKE]
[STRIKE]I've uploaded a screenshot of the graph that I'm referring to (as an attachment to this thread) so that you don't have to run the program hopefully.[/STRIKE]
EDIT: It's just a coincidence the graphed coefficients happen to resemble the original function (sawtooth(x)). I changed y and y_test to equal sin(x) and the same coefficient graph appears. Can anybody give me a better algorithm for modeling the Fourier coefficients? I guess I've been working on this too much, I can't seem to be able to figure it out. I've also uploaded the graph.
Heres my code:
Any help is greatly appreciated!
The problem with it: [STRIKE]it gives a graph that has a different period and amplitude than the original function (although its the same general shape).[/STRIKE]
[STRIKE]I've uploaded a screenshot of the graph that I'm referring to (as an attachment to this thread) so that you don't have to run the program hopefully.[/STRIKE]
EDIT: It's just a coincidence the graphed coefficients happen to resemble the original function (sawtooth(x)). I changed y and y_test to equal sin(x) and the same coefficient graph appears. Can anybody give me a better algorithm for modeling the Fourier coefficients? I guess I've been working on this too much, I can't seem to be able to figure it out. I've also uploaded the graph.
Heres my code:
Code:
%% I_A
% BEGIN SOME FUNCTION AND VARIABLE DECLARATIONS
syms x;
length_of_k = 25; % Number of coefficients to calculate
p = pi; % Function period
y = sin(x); % Function
x_test = -p : 1/25 : 2*p; % Original x values
y_test = sin(x_test); % Original f(x)
% END SOME FUNCTION
% BEGIN COMPUTING FOURIER COEFFICIENTS
% -- BEGIN NOTES --
% Calculate : a_0, a_k, b_k with k > 0
% a_0 = (1/p)*int(f(t), t, 0, p) -- Integral f(t) w.r.t. t from 0 to p
% a_k = (2/p)*int(f(t)*cos((2*pi*k*t)/p), t, 0, p)
% b_k = (2/p)*int(f(t)*sin((2*pi*k*t)/p), t, 0, p)
% -- END NOTES --
a_0 = (1/p)*int(y, x, 0, p); % Calculate as priming reed
a_coeff = []; % Declaring null array
b_coeff = []; % Declaring null array
fprintf('Fourier Coefficient:\ta_0 ==> %0.2f\n', double(a_0))
for k = 1 : length_of_k
a_coeff = [a_coeff, (2/p)*int(x*cos(2*pi*k*x/p), x, 0, p)];
b_coeff = [b_coeff, (2/p)*int(x*sin(2*pi*k*x/p), x, 0, p)];
fprintf('Fourier Coefficient:\t');
fprintf('a_%1.0f ==> %0.3f\t\t', k, double(a_coeff(k)));
fprintf('b_%1.0f ==> %0.3f\n', k, double(b_coeff(k)));
end
% END COMPUTING FOURIER COEFFICIENTS
% BEGIN GENERATING FOURIER TERMS
fs_x = [];
fs_a0_calc = (a_0/2);
for i = 1 : length(x_test)
a_calc = 0;
b_calc = 0;
for k = 1 : length_of_k
a_calc = a_calc + a_coeff(k)*cos(k*x_test(i));
b_calc = b_calc + b_coeff(k)*sin(k*x_test(i));
end
fs_x = [fs_x, fs_a0_calc + a_calc + b_calc];
end
% END GENERATING FOURIER TERMS
% BEGIN PLOTS
plot(x_test, y_test, 'b', x_test, fs_x, 'r'); % Plot the original function
grid on; % Turn on grid
% END PLOTS
% BEGIN DEBUGGING CODE
fprintf('Max of f(x) = %0.4f\n', max(y_test));
fprintf('Min ox f(x) = %0.4f\n', min(y_test));
fprintf('Max of FS[x] = %0.4f\n', max(double(fs_x)));
fprintf('Min of FS[x] = %0.4f\n', min(double(fs_x)));
% END DEBUGGING CODE
Any help is greatly appreciated!
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