df=5;fi0=4.938;fi1=.672;fi2=14.052;fi3=2.1*10^(-4);
l=4250
x=5:5:l;
for i=1:length(x)
y(i)=fi0+fi1*(1-2.71^(-i/fi2))-fi3*i;
end
z=(1/pi).*y;
plot(x,z)