Why is line does not showing up on the plot?

Question

Ray Malifalitiko 2020-11-13

0
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编辑： Cris LaPierre 2020-11-13

I'm trying to plot a line but it's not working. Here's an example of what doesn't work:

c = 3*10^8;
f0 = 10^9;
Vtarget = 10;
Vradar = 0;
fd = 2*(Vradar - Vtarget).*f0./c;
t= 0:100;
plot(t,fd)
title('Doppler Frequency Change')
xlabel('Time(sec)')
ylabel('Doppler Frequency(Hertz)')

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Answer 1

Ameer Hamza 2020-11-13

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编辑：Ameer Hamza 2020-11-13

在 MATLAB Online 中打开

t is a vector, whereas fd is a scalar. How do you want to plot these two? As a straight line? If yes, then try this

c = 3*10^8;
f0 = 10^9;
Vtarget = 10;
Vradar = 0;
fd = 2*(Vradar - Vtarget).*f0./c;
t= 0:100;
plot(t,fd*ones(size(t)))
title('Doppler Frequency Change')
xlabel('Time(sec)')
ylabel('Doppler Frequency(Hertz)')

You can also use yline()

c = 3*10^8;
f0 = 10^9;
Vtarget = 10;
Vradar = 0;
fd = 2*(Vradar - Vtarget).*f0./c;
t= 0:100;
yline(fd)
title('Doppler Frequency Change')
xlabel('Time(sec)')
ylabel('Doppler Frequency(Hertz)')

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Answer 2

Cris LaPierre 2020-11-13

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编辑：Cris LaPierre 2020-11-13

在 MATLAB Online 中打开

Because fd contains a single value. This defines a point, not a line. Therefore, your code plots a single point at each t value, but they are not connected. You can see this by adding a line format spec that includes a marker to your plot command.

c = 3*10^8;

f0 = 10^9;

Vtarget = 10;

Vradar = 0;

fd = 2*(Vradar - Vtarget).*f0./c;

t= 0:100;

plot(t,fd,'r-o')

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