How drawing a rectangle in a semilog plot ?

I try to draw a transparent rectangle in a semilog plot,

With the function fill and the propertie 'FaceAlpha" it work with a linear plot

but don't work in a semilogx plot !!!

more over, I don't find help about 'FaceAlpha' properties.

an example:

clear all;
close all;
c=[0.6 0 1];

figure;
hold on;
plot(cumsum(ones(1,100)),0.25*cumsum(ones(1,100)),'r');
fill([1 1 50 50], [0 10 10 0],c, 'FaceAlpha', 0.4,'EdgeColor','none');
grid on;

figure;
hold on;
set(gca,'XScale','log');
plot(cumsum(ones(1,100)),0.25*cumsum(ones(1,100)),'r');
fill([1 1 50 50], [0 10 10 0],c, 'FaceAlpha', 0.4,'EdgeColor','none');
grid on;

Answer 1

[Walter Roberson]

Unfortunately you will not be able to do transparency with log plots (unless the situation changed as of R2014b): http://www.mathworks.com/matlabcentral/newsreader/view_thread/241372

fill() is documented as creating patch() objects and the fill documentation references patch properties which defines FaceAlpha