Errors when using fitnlm

I am trying to use the fitnlm function and I keep getting this set of errors

In nlinfit>LMfit (line 579)
  In nlinfit (line 276)
  In NonLinearModel/fitter (line 1123)
  In classreg.regr.FitObject/doFit (line 94)
  In NonLinearModel.fit (line 1430)
  In fitnlm (line 94) 
Warning: Rank deficient, rank = 6, tol =  2.853427e-11. 
Error using nlinfit>checkFunVals (line 641)
The function you provided as the MODELFUN input has returned Inf or NaN values.

Error in nlinfit>LMfit (line 588)
    if funValCheck && ~isfinite(sse), checkFunVals(r); end

Error in nlinfit (line 276)
        [beta,J,~,cause,fullr] = LMfit(X,yw, modelw,beta,options,verbose,maxiter);

Error in NonLinearModel/fitter (line 1123)
                    nlinfit(X,y,F,b0,opts,wtargs{:},errormodelargs{:});

Error in classreg.regr.FitObject/doFit (line 94)
            model = fitter(model);

Error in NonLinearModel.fit (line 1430)
            model = doFit(model);

Error in fitnlm (line 94)
model = NonLinearModel.fit(X,varargin{:});

Here is how I am calling the function (n13 is a single y variable, n_x is a 212x4 matrix of x variables, I have tried both versions of "modelfun" and neither works)

%modelfun = @(b,n_x)b(1) + b(2)*n_x(:,1).^b(3) + b(4)*n_x(:,2).^b(5) + b(6)*n_x(:,3).^b(7) + b(8)*n_x(:,4).^b(9);
modelfun = 'n13~b0+b1*x1^b2+b3*x2^b4+b5*x3^b6+b7*x4^b8';
beta0=ones(9,1);
NLM_n = fitnlm(n_x,n13,modelfun,beta0);

Not sure what the problem is. Any help would be great!

Answer 1

[oyun kwon]

Could you try adding '.' between parameter connetion part?

such as

your code

modelfun = 'n13~b0+b1*x1^b2+b3*x2^b4+b5*x3^b6+b7*x4^b8';

suggested code

modelfun = 'n13~b0+b1.*x1.^b2+b3.*x2.^b4+b5.*x3.^b6+b7.*x4.^b8';