plot with 2 x-axes (logscale)

Hi all, I am currently trying to plot with two x-axes. I tried the plotxx.m from File Exchange (thanks for sharing), but still don't get it... I have a dataset x1 and y1 to plot on loglog-scale. In addition, I want to add a 2nd x-axes (on top) which is not! log-scale. I actually have no 2nd dataset to plot, but can of course apply x1 (then x1*) and y1 again. Anyone who as an idea how to do that?

[ax,h1,h2] = plotxx(x1,y1,x1*,y1); set(ax(1),...

Thanks in advance, Franziska