Plotting Cos complete stupidity

I have been plotting trig functions like this for years in matlab with zero problem Now all of a sudden it no longer works.

x = [0:.1:20]
y = .5*cos(2*pi*60.*x)
plot(x,y)

Now today all i get is a constant value. What is going on here

Doing the following makes no difference

x = [0:.1:20]
plot(x,.5*cos(2*pi*60.*x))

Someone please tell me why in the holy land of matlab multiplying the vector X by a constant of 2*pi*60 completely ruins the plot and turns it into a constant. It makes zero sense!

but yet somehow this works

plot(x,cos(x))

All I'm doing is multiplying the foreign X by a constant of 2*pi*60 This is ridiculous

Also just to add the following works

y = cos(2*x) y = cos(2*pi*x)

But for some insane reason the plot goes nuts when you plot

y = cos(2*pi*60*x) and says the plot is a constant .5

Also just to add to the infuriation of this if you plot

plot(x,.5*cos(120*pi*x)) %you get a constant of .5
plot(x,.5*cos(119*pi*x)) %you get a proper oscillating cos

Answer 1

[Massimo Zanetti]

This is not ridiculous, this is math.

Try refine the step of x:

x = 0:.01:20;
y = .5*cos(2*pi*60*x);
plot(x,y)

Your "weird" phenomenon is due to the fact that all cosine crests fall into the discretized interval you choose, which is too coarse to make you see them.

[Robert]

great so i loose an hour worth of work today because a 1 in million chance my interval falls exactly on a constant Awesome!