Nonlinier Regression withExponential Approach.

I want to develop an equation from Nonlinier Regression withExponential Approach. My code like this: b1=2; b2=3; b3=0.01; b4=0.25; b5=0.0001; beta0=[b1 b2 b3 b4 b5]; X1=[ones(size(Amax1)) Amax1 Mw1 Vs1 Depth1 Distance1]; Y1=[Ym1]; mdlA = NonLinearModel.fit(X1,Y1,modelfun,beta0) I want to add bootsrap for estimating standard deviation.

yfit=X1*mdlA; resid=Y1-yfit; se= std(bootstrp(regress(yfit+bootr,X1),resid));

The answer is:

Undefined function 'mtimes' for input arguments of type 'NonLinearModel'.

Error in NLRegression (line 33) yfit=X1*mdlA;

Is there any person can help me to do some Nonlinier Regression with exponential approach and combine with Bootstrap.