信号与系统matlab答案.docx

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M2-3 (1) function yt=x(t) yt=(t).*(t>=0&t<=2)+2*(t>=2&t<=3)-1*(t>=3&t<=5); (2)function yt=x (t) yt=(t).*(t>=0&t<=2)+2*(t>=2&t<=3)-1*(t>=3&t<=5); t=0:0.001:6; subplot(3,1,1) plot(t,x2_3(t)) title(x(t)) axis([0,6,-2,3]) subplot(3,1,2) plot(t,x2_3(0.5*t)) title(x(0.5t)) axis([0,11,-2,3]) subplot(3,1,3) plot(t,x2_3(2-0.5*t)) title(x(2-0.5t)) axis([-6,5,-2,3]) 图像为： M2-5 (3) function y=un(k) y=(k>=0) untiled3.m k=[-2:10] xk=10*(0.5).^k.*un(k); stem(k,xk) title(x[k]) axis([-3,12,0,11]) M2-5 (6) k=[-10:10] xk=5*(0.8).^k.*cos((0.9)*pi*k) stem(k,xk) title(x[k]) grid on M2-7 A=1; t=-5:0.001:5; w0=6*pi; xt=A*cos(w0*t); plot(t,xt) hold on A=1; k=-5:5; w0=6*pi; xk=A*cos(w0*0.1*k); stem(k,xk) axis([-5.5,5.5,-1.2,1.2]) title(x1=cos(6*pi*t)&x1[k]) A=1; t=-5:0.001:5; w0=14*pi; xt=A*cos(w0*t); plot(t,xt) hold on A=1; k=-5:5; w0=14*pi; xk=A*cos(w0*0.1*k); stem(k,xk) axis([-5.5,5.5,-1.2,1.2]) title(x2=cos(14*pi*t)&x2[k]) A=1; t=-5:0.1:5; w0=26*pi; xt=A*cos(w0*t); plot(t,xt) hold on A=1; k=-5:5; w0=26*pi; xk=A*cos(w0*0.1*k); stem(k,xk) axis([-5.5,5.5,-1.2,1.2]) title(x1=cos(26*pi*t)&x1[k]) M2-9 (1) k=-4:7; xk=[-3,-2,3,1,-2,-3,-4,2,-1,4,1,-1]; stem(k,xk,file) (2) k=-12:21; x=[-3,0,0,-2,0,0,3,0,0,1,0,0,-2,0,0,-3,0,0,-4,0,0,2,0,0,-1,0,0,4,0,0,1,0,0,-1]; subplot(2,1,1) stem(k,x,file) title(3倍内插) t=-1:2; y=[-2,-2,2,1]; subplot(2,1,2) stem(t,y,file) title(3倍抽取) axis([-3,4,-4,4]) (3) k=-4:7; x=[-3,-2,3,1,-2,-3,-4,2,-1,4,1,-1]; subplot(2,1,1) stem(k+2,x,file) title(x[k+2]) subplot(2,1,2) stem(k-4,x,file) title(x[k-4]) (4) k=-4:7; x=[-3,-2,3,1,-2,-3,-4,2,-1,4,1,-1]; stem(-fliplr(k),fliplr(x),file) title(x[-k]) M4-1 （1）对于周期矩形信号的傅里叶级数cn =-1/2j*sin(n/2*pi)*sinc(n/2) n=-15:15; X=-j*1/2*sin(n/2*pi).*sinc(n/2); subplot(2,1,1); stem(n,abs(X),file); title(幅度谱) xlabel(nw); subplot(2,1,2); stem(n,angle(X),file); title(相位谱) （2）对于三角波信号的频谱是：Cn=-4n2π2+2nπsinnπ2+4n2π2cosnπ2 n=-15:15; X=sinc(n)-0.5*((sinc(n/2)).^2); subplot(2,1,1); stem(n,abs(X),file); title(幅度谱) xlabel(nw); subplot(2,1,2); stem(n,angle(X),file); title(相位谱) M4-4 (1) tau=0.5;T=100;N=T/tau; t=[0:tau:(T-tau)]; x=(t>=0 & t<=2).*1; X=fftshift(tau*fft(x)); w=-(pi/tau)+(0:N-1)*(2*pi/(N*tau)); plot(w,X) grid on (4) tau=0.1;T=50;N=T/tau; t=[0:tau:(T-tau)]; x=(t>=0).*exp(-t); X=fftshift(tau*fft(x));X=abs(X); w=-(pi/tau)+(0:N-1)*(2*pi/(N*tau)); plot(w,X) grid on