How can I label the same line using different color

Hi, everyone,

I want describe the same line by different colors, for exaple,

a=0:0.01:2*pi; b=sin(a); plot(a,b,'r')

however, how to make the sine line red when its value is more than zero while

black if its value is less than zero.

Thanks.

Answer 1

[Matt Fig]

One way to get the effect is to use two lines.

a = 0:0.01:2*pi; 
b = sin(a);
b2 = b;
b(b<=0) = nan;  % nan values are not plotted.
b2(b2>=0) = nan;
plot(a,b,'r',a,b2,'k')