Calculate Moment Generating Function
tau = FracScalExp(z,a,loscale,hiscale)
matrix nexp by nscale of z(q,a) ``Thermo Partition Func''
list of scales
optional min scale to fit line by
optional max scale to fit line by
vector 1 by nscale of moments
tau(q) = Slope [ log(z(q,a)) versus log(a) ] section 6.5.2 of Mallat's book