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Periodic functions show up as a straight line

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Hieu Nguyen
Hieu Nguyen 2017-11-2
评论： KSSV 2017-11-2
Hello everyone!
When I plot the multiplots in one figure, only x1 shows up as a true graph of a periodic function, the rest shows up as straight lines. It is true for x0 as a straight line as it is a constant function. What goes wrong in my code? Thank you in advance.
t = 0:0.000001:2;
x0 = 0.0507*cos(0*pi*t);
figure
plot(t,x0)
set(gca,'fontsize',13)
title('Plot 1:Spanning over one period')
hold on
x1 = 0.645*cos(pi*t - 3.14/2);
plot(t,x1)
x3 = 0.00057*cos(3*pi*t - 3.116);
plot(t,x3)
x5 = 0.0000684*cos(5*pi*t - 3.126);
plot(t,x5)
legend('x0','x1','x3','x5')
xlabel('time t (second)')
ylabel('x(t) in meter')
hold off
  2 个评论
KSSV
KSSV 2017-11-2
All expect x0 periodic functions.....but the amplitude of them is low....compared to the amplitude of x1....that's why it shows up like straight line.
Hieu Nguyen
Hieu Nguyen 2017-11-2
Can I fix that? It seems odd, but what you explained to me makes sense.

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回答（1 个）

Walter Roberson
Walter Roberson 2017-11-2
You have
x0 = 0.0507*cos(0*pi*t);
which is going to be cos(0) * 0.0507 = 0.0507 for all t -- a straight line.
You have
x1 = 0.645*cos(pi*t - 3.14/2);
which successfully plots as expected.
You have
x3 = 0.00057*cos(3*pi*t - 3.116);
which has a maximum amplitude of 0.00057 which is too small an amplitude change to show up unless you zoom in.
You have
x5 = 0.0000684*cos(5*pi*t - 3.126);
which is about an 8 time smaller amplitude yet, and would need even more zooming in to so.
  2 个评论
Hieu Nguyen
Hieu Nguyen 2017-11-2
how can I zoom in? is there a command in matlab allowing me to do that? Thanks!
KSSV
KSSV 2017-11-2
There would be magnifying glass symbol on the plot ...click on it.....

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