PLotting noisy signal matlab

Suppose the sampling interval is pi/100.

 t = 0:pi/100:40;
 x = cos(pi/10*t)+0.5*randn(size(t));
 plot(t,x)Then you know where pi/2, 3pi/4 etc are.

t(50) is pi/2 and x(50) is the signal value at t=pi/2

plot(t,x); hold on plot(t(50),x(50),'r^','markerfacecolor',[0 0 0],'markersize',10); plot(t(75),x(75),'r^','markerfacecolor',[0 0 0],'markersize',10); and so on.

Suppose t was a vector and for each element is the one that I want to plot, so for instance, t(1), t(2),..., and so on. How would you do this?

Answer 1

[Wayne King]

What do you mean suppose t was a vector?

 t = 0:pi/100:40;
 x = cos(pi/10*t)+0.5*randn(size(t));
 plot(t,x)

t is a vector in the above. So is x and you are plotting the vector x as a function of the vector t.

[T]

What if t(1) = 0.4, t(5) = 0.5, t(6)=0.6, ....and so on. If I only wanted to plot x at t(1), t(5),.... ,, how would you do this?

x(t(1)) won't give me that result.

Answer 2

[Wayne King]

You can subset your vector, for example:

    t = 0:.01:1-0.01;
    x = cos(2*pi*10*t);
    plot(t,x)

Now the spacing in my t vector is 0.01 seconds. What if I wanted to only plot at time intervals of 0.1 seconds? Since the sine wave has a frequency of 10 Hz, I'll get a constant function.

   tnew = t(1:10:end);
   xnew = x(1:10:end);
   plot(tnew,xnew)

[T]

Sorry, I should have been less ideal. What if t(1) = 0.5235, t(2) = 0.6743, t(3)=.756 and so on?

Answer 3

[Richard Zapor]

If you want a specific set of points a third vector can be created, v=[1 4 9 12]; The plot(t(v),x(v)) will only use the subset points.

If you desire time values not part of the original data set then use interp1. xi=[.5235 .6743 .756]; yi=interp1(t,x,xi);plot(xi,yi)

For markers: plot(t,x); hold on; plot(t(5:10:100),x(5:10:100),'r^','markerfacecolor',[0 0 0],'markersize',10);