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+//Example 6_13:
+//Discrete Time Fourier Transform of discrete sequence x[n]=(n)*(a^n).u[n], a>0 and a<0
+clear;
+clc;
+close;
+//DTS Signal
+a1=0.5;
+a2=-0.5;
+max_limit=10;
+for n=0:max_limit-1
+x1(n+1)=(n)*(a1^n);
+x2(n+1)=(n)*(a2^n);
+end
+n=0:max_limit-1;
+Wmax=2*%pi;
+K=4;
+k=0:(K/1000):K;
+W=k*Wmax/K;
+x1=x1';
+x2=x2';
+XW1=x1*exp(-sqrt(-1)*n'*W);
+XW2=x2*exp(-sqrt(-1)*n'*W);
+XW1_Mag=abs(XW1);
+XW2_Mag=abs(XW2);
+W=[-mtlb_fliplr(W),W(2:1001)];
+XW1_Mag = [mtlb_fliplr(XW1_Mag),XW1_Mag(2:1001)];
+XW2_Mag = [mtlb_fliplr(XW2_Mag), XW2_Mag(2:1001)];
+[XW1_Phase,db] = phasemag(XW1);
+[XW2_Phase,db] = phasemag(XW2);
+XW1_Phase = [-mtlb_fliplr(XW1_Phase),XW1_Phase(2:1001)];
+XW2_Phase = [-mtlb_fliplr(XW2_Phase),XW2_Phase(2:1001)];
+figure
+subplot(3,1,1);
+plot2d3('gnn',n,x1);
+xtitle('Discrete Time Sequence x[n] for a>0')
+subplot(3,1,2);
+a = gca();
+a.y_location ="origin";
+a.x_location ="origin";
+plot2d(W,XW1_Mag);
+title('Magnitude Response abs(X(jW))')
+subplot(3,1,3);
+a = gca();
+a.y_location ="origin";
+a.x_location ="origin";
+plot2d(W,XW1_Phase);
+title('Phase Response <(X(jW))')
+//plot for a<0
+figure
+subplot(3,1,1);
+plot2d3('gnn',n,x2);
+xtitle('Discrete Time Sequence x[n] for a>0')
+subplot(3,1,2);