Hello Tony,
Just read the Tutorials and Examples on Wiki regarding plotting in SMath. There is a difference in SMath between plotting 2D graphs as a function or plotting a two column matrix.
Here is your example when you wanted to plot the function M for the given range of fs, therefore to plot a two column matrix - first collum is x-axis and the second column is y-axis. I hope you would understand it.
I've just made up the needed parameters - do not know their values because you did not proved them.

Regards,
Radovan
When Sisyphus climbed to the top of a hill, they said: "Wrong boulder!"