How to plot a smooth graph?

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donghun lee
donghun lee on 2 Apr 2020
Commented: donghun lee on 2 Apr 2020
clc,clear all
b0 = 0.015;
b1 = 0.015;
b2 = 0.035;
b3 = 0.050;
v = 40; %velocity
L = 2;
w = (2*pi*v)/L; %angular frequency
F = w*(1/(2*pi)); %in Hz
t = linspace(0,10,18);
b = b0 + b1*sin(w*t) + b2*sin(2*w*t)
+b3*sin(3*w*t);
plot(t,b)
Hi, I want to make this graph as being a smooth graph.
Thank you for your time.
  1 Comment
Rik
Rik on 2 Apr 2020
Although you could resample your function to draw a smooth curve through your data points, that would not accurately describe your function. You can greatly increase the number of points in your t vector to see that you have an enormous amount of aliasing going on here. See this Wikipedia page for more information.

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Accepted Answer

Birdman
Birdman on 2 Apr 2020
Edited: Birdman on 2 Apr 2020
You need to increase the step size of your t vector:
t = linspace(0,10,100);
Code:
b0 = 0.015;
b1 = 0.015;
b2 = 0.035;
b3 = 0.050;
v = 40; %velocity
L = 2;
w = (2*pi*v)/L; %angular frequency
F = w*(1/(2*pi)); %in Hz
t = linspace(0,10,100);
b = b0 + b1*sin(w*t)+b2*sin(2*w*t)+b3*sin(3*w*t);
plot(t,b)
  5 Comments
Rik
Rik on 2 Apr 2020
That is why I suggested to zoom in. The weirdness is not from me, but actually from your function. If you want a true plot of your function you should increase the number of samples until further increasing it no longer changes your graph. For this function that starts at about 2500 samples. With about 10000 samples I no longer notice an improvement in smoothness.
You could avoid having to do this yourself by using fplot:
b0 = 0.015;
b1 = 0.015;
b2 = 0.035;
b3 = 0.050;
v = 40; %velocity
L = 2;
w = (2*pi*v)/L; %angular frequency
F = w*(1/(2*pi)); %in Hz
t_max=10;
b_fun =@(t) b0 + b1*sin(w*t)+b2*sin(2*w*t)+b3*sin(3*w*t);
fplot(b_fun,[0 t_max])
axis([0 1 -0.125 0.125])%zoom in to see detail
donghun lee
donghun lee on 2 Apr 2020
Ah!! Thank you soooo much for your help. I got what you mean now! I really appreciate it.
Thank you for your time again Rik!

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More Answers (1)

Walter Roberson
Walter Roberson on 2 Apr 2020
t = linspace(0,10,18);
Increase the 18 to something larger, such as 50.

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