1. Read in arrays x and y from
file xyL.dat,
and find the best 5^{th}degree polynomial fit
xy = ReadList["xyL.dat",{Number,Number}];
Fit[ xy, {x^5, x^4, x^3, x^2, x^1, 1}, x]

2. Read in arrays x and y from
file xyN.dat,
and find the best fit to
y(x) = a exp(bx)
sin(cx + d)
xy = ReadList["xyN.dat",{Number,Number}];
Needs["Statistics`NonlinearFit`"]
YofX[x_] = a Exp[b x] Sin[c x + d]
initialguesses = {{a,0.5}, {b,0.5},{c,1.5},{d,0.5}}
ft = NonlinearFit[xy, YofX[x], x, initialguesses]
Plot[ft, {x,0,20}];

