Articificially creat a fuzzt data set {x_i,y_i} based on a defined function and then export it as
“functiondata.dat”

SetDirectory[NotebookDirectory[]];
(* define your function here *)
a=6.7;
y[x_]:=a*x^2
(* end of define your function here *)
(*define the domain *)
NP=1000; (* number of points along the x-axis from xini to xlast *)
xini=-10;xlast=10;Deltax=(xlast-xini)/NP;
(*end of define the domain *)

txy=Table[{x+(2Random[]-1)^3,y[x]+(2Random[]-1)^3},{x,xini,xlast,Deltax}];
lpttxy=ListPlot[txy,AxesLabel->{"x","y"}]
txy
Export["functiondata.dat",txy];