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+//Graphical//

+//Example 4.1.2 Continuous Time Fourier Transform

+//and Energy Density Function of a Square Waveform

+// x(t)= A, from -T/2 to T/2

+clear;

+clc;

+close;

+// Analog Signal

+A =1;    //Amplitude

+Dt = 0.005;

+T = 4;  //Time in seconds

+t = -T/2:Dt:T/2;

+for i = 1:length(t)

+  xa(i) = A;

+end

+//

+// Continuous-time Fourier Transform

+Wmax = 2*%pi*2;        //Analog Frequency = 2Hz

+K = 4; k = 0:(K/800):K;

+W = k*Wmax/K;

+disp(size(xa))

+Xa=xa'*exp(-sqrt(-1)*t'*W)*Dt;

+Xa = real(Xa);

+W = [-mtlb_fliplr(W), W(2:501)]; // Omega from -Wmax to Wmax

+Xa = [mtlb_fliplr(Xa), Xa(2:501)];

+ESD = Xa^2;  //Energy Density Spectrum

+subplot(3,1,1);

+plot(t,xa);

+xlabel('t in msec.');

+ylabel('xa(t)')

+title('Analog Signal')

+subplot(3,1,2);

+plot(W/(2*%pi),Xa);

+xlabel('Frequency in Hz');

+ylabel('Xa(jW)')

+title('Continuous-time Fourier Transform')

+subplot(3,1,3);

+plot(W/(2*%pi),ESD);

+xlabel('Frequency in Hz');

+ylabel('SXX')

+title('Energy Density Spectrum')