I would like to draw two x axes with ticks and legends in the bottom and top axes where one axis is a linear transformation of the other for the same y range. There is a similar application described in section 4.8.10 of the pgfplots manual for two y axes. Are two x axes possible using the axis environment?
As a default, both axes are plotted left/right & top/bottom. That’s why you get both ticks on the upper axis (I assume that is what you meant). You need to explicitly tell pgfplots you don’t want the upper part of the x-axis in the first