The plots now all work! Also spotted that I needed a different flexp parameter for the Zsubload, so put that in and the plot scale was all sorted. Bit fiddly but got there in the end :) Thanks for the help on this, still pretty new with using Maple so it takes a little getting used to.
The equations relate to different isostatic models of the Earth's lithosphere (the Crust and uppermost mantle) to see how they vary with wavelength and the admittance function (Z(k) )=fft(gravity)/fft(topography). The actual equations simplify to more usable structures.
I am a geologist by training and currently completing a PhD in geodynamics.
The equations are found in the book by Tony Watts - Isostasy and flexure of the lithosphere (2001)
Have some more complex functions to work on in Maple so will give those a try later on. Early days with Maple and I am sure I will have more queries as I learn it more.
Thanks again for the help