transparency line of polar graph

I plot a polar graph with line data set. I could not change transparency of data lines, i tried facealpha and edgealpha but they did not work.

if anyone has a idea that how can change the transperancy of lines would be great, thank you.

Answer 1

[Chunru]

theta = deg2rad(0:360);
r = cos(theta).^2;
a = polar(theta, r);
a.Color =[1,0,0, .2]; % use the last value to control the transparency

[Begüm DEVLET]

it works, thanks!