How can I remove the error " Not enough input arguments" of nlinfit?

Hello everybody. This is my code:

clc;clear;close all;

x=0:.1:2*pi;
y=sin(x);
pp=spline(x,y);
k=4;
t=x;

xq=x;


for i=1:length(y)-1
    cc(:,i)=pp.coefs(i,1).*(x-pp.breaks(i)).^(k-1) + pp.coefs(i,2).*(x-pp.breaks(i)).^(k-2) +...
        pp.coefs(i,k-1).*(x-pp.breaks(i)) + pp.coefs(i,k);
end
for i=1:length(y)-1
    modelfun = @(x,a,b,c,d)(a(i).*(x-1)).^(k-1) + b(i).*(x-1).^(k-2) +c(i).*(x-1)+d(i);
    rng('default') % For reproducibility
    
    a(i)=pp.coefs(i,1);
    b(i)=pp.coefs(i,2);
    c(i)=pp.coefs(i,3);
    d(i)=pp.coefs(i,4);
    a0(i)=a(i);
    b0(i)=b(i);
    c0(i)=c(i);
    d0(i)=d(i);
    x = exprnd(2,63,1)';
    z(i,:) = modelfun(x,a(i),b(i),c(i),d(i)); 
    
    beta0(i,:)=[a0(i),b0(i),c0(i),d0(i)];
    opts = statset('nlinfit');
    opts.RobustWgtFun = 'bisquare';
    beta(i)=nlinfit(x,z(i,:),modelfun,beta0(i,:),opts)
    
    ci(i) = bootci(1000,{beta(i),x,z(i,:)},'Type','norm')
    
end

Answer 1

[KSSV]

Replace your modelfunction with:

 modelfun = @(x,b)(b(1)*(x-1)).^(k-1) + b(2)*(x-1).^(k-2)+b(3)*(x-1)+b(4);