How to create positive or negative half cycle of sine wave?

I got a full cycle of sine wave. if I need to zero the 1st half of the sine wave , to get only the negative half cycle, what should I do ?I have done this:

close all;
clc;
t=[0 0 0 0 0 1 1.2 1.4 1.6 1.8 2]
f=.5;% Input Signal Frequency
x=sin(2*pi*f*t);% Generate Sine Wave  
plot(t,x);

I wanted an improved version . Is there any other way to do it ?

Answer 1

[Star Strider]

Yes. Rectify it using logical indexing:

t = 0:0.2:2;
f=.5;% Input Signal Frequency
x=sin(2*pi*f*t);% Generate Sine Wave  
x(x>0) = 0;                       % Rectified Sine Wave
plot(t,x);
axis([xlim    -1  1])

Answer 2

[Olexander Zhytenko]

I have a different version (see answer file).