What happened to plotxx?

I am trying to plot four different curves with two x scales. One x axes labeled on top, one on bottom of the figure. I am aware of plotyy, but there doesn't seem to be a plotxx equivalent. How do I plot curves on two different x scales on the same curve?

Answer 1

[Star Strider]

It’s hiding in the plotyy documentation as a link to Graph with Multiple x-Axes and y-Axes.

Answer 2

[KAE]

There is also a plotxx in the File Exchange.