MATLAB: Function works with lsqcurvefit but not nlinfit

nlinfit; lsqcurvefit; betainc

I'm attempting to get a nonlinear least squares fit for the following function:
Nloc = 250;
d = 1 / Nloc;
m = 0.5; %Initial guess
ncmfun = @(m, p) arrayfun(@(p) betainc(d, Nloc*m .* p, Nloc*m .* (1 - p), 'upper'), p);
Where m is the parameter being fit, Nloc and d are constants, and p and freq are vectors of positive real numbers and of the same length (I triple checked). When I use lsqcurvefit everything works fine:
[mfit,resnorm,]  = lsqcurvefit(ncmfun, m, p, freq, 0, 1)
Also, if I use any m to evaluate the function, everything works fine as well.
However when I use nlinfit:
[mfit,R,Jac,CovB,MSE,ErrorModelInfo] = nlinfit(p, freq, ncmfun, m)
I get the following error(s):
Error using betainc
Z must be real and non-negative.
Error in @(p)betainc(d,Nloc*m.*p,Nloc*m.*(1-p),'upper')
Error in
@(m,p)arrayfun(@(p)betainc(d,Nloc*m.*p,Nloc*m.*(1-p),'upper'),p)
Error in nlinfit>@(b,x)w.*model(b,x) (line 206)
        modelw = @(b,x) w.*model(b,x);
Error in nlinfit>LMfit (line 486)
    yfit = model(beta,X);
Error in nlinfit (line 207)
        [beta,J,~,cause,fullr] = LMfit(X,yw,
        modelw,beta,options,verbose,maxiter);
Error in Sloan_NCM_Parameterize_Nm (line 37)
[mfit,R,Jac,CovB,MSE,ErrorModelInfo] = nlinfit(p, freq,
ncmfun, m);
What's especially frustrating was this same script was working a couple weeks ago. I then tried to use it again and it no longer works. I tried to go through and see if I accidentally changed something and didn't remember, but I can't find any errors. Furthermore, I'm confused as to why lsqcurvefit works but not nlinfit. I'd like to use nlinfit because it provides me with more statistical information about the error.
Thanks in advance for any help you can provide!

Best Answer

In LSQCURVEFIT, you are constraining the estimate of m to lie between 0 and 1, which always satisfies the input requirements of betainc. You are not doing likewise in NLINFIT. Judging from your error message "Z must be real and non-negative", the iterations over m in NLINFIT are undoubtedly straying into the negative range, resulting in negative Z inputs to betainc.
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