# Don't get what is happening in matlab sin() function. need to know difference between sin(2*50*pi*t) and sin(2*1*pi*t)

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AK Nahin on 9 Sep 2022
Answered: William Rose on 9 Sep 2022
Hi,
I am using Matlab to plot the sin graph. But when I put sin(2*50*pi*t) it shows something else than the sinusoidal curve. Can you please help me to find out why it is happening? Thanks in advance.
Code:
t = 0:0.1:20;
x = sin(2*50*pi*t);
y = sin(2*1*pi*t);
subplot(2,1,1)
plot(t,x)
subplot(2,1,2)
plot(t,y)
Steven Lord on 9 Sep 2022
It wouldn't help in this case but if you're computing the sine of pi times some angle, consider using the sinpi function instead of explicitly computing pi times the angle and calling sin.

Torsten on 9 Sep 2022
t1 = 0:0.001:1;
x = sin(2*50*pi*t1);
t2 = 0:0.1:1;
y = sin(2*1*pi*t2);
subplot(2,1,1)
plot(t1,x)
subplot(2,1,2)
plot(t2,y)
William Rose on 9 Sep 2022
OK will do.

William Rose on 9 Sep 2022
In your original code, you were evaluating sin(t) at integer multiples of pi, and therefore sin(t)=0 at each point. Due to round-off error, the values are not exactly zero, but are <10^-12.
@Torsten demonstrates that by changing the values of t, you can see that it is a normal sine wave.

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