信号与系统 matlab答案

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=-4

n2π2+

2

nπ

sin nπ

2

+

4

n2π2

cos nπ

2

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')