急求用matlab进行指数函数的最小二乘拟合

m=[99,139,199,299]';
n=[0.35,0.25,0.2,0.15]';
%拟合n=ae^(bm)模型
s = fitoptions('Method','nonlinearLeastSquares',...
'Lower',[0.4,-1e-2],...
'Upper',[1.2,-1e-8] ,...
'startpoint',[0.5 -0.0001]);
f = fittype('a*exp(b*x)','options',s);
[c2,gof2] = fit(m,n,f)
plot(m,n,'o'); hold on
plot(c2);