Figure 1: PAL_PFML_Fit first performs a brute-force search across a discrete parameter space, then uses best
function in the grid as starting point in the iterative search procedure. Threshold and slope are free parameters.
Figure 2: Same as above, but now the lapse rate is also a free parameter. (Note that any combination of
the 4 parameters of the PF can be included in the search grid (including all 4!)).