in curve fitting of linear sinusoidal function with polynomial of 4th degree, the error popping up is define b and x_l

I am new to matlab. I would appreciate to sort this out of curve fitting algorithm of linear sinusoidal function with polynomial of 4th degree

m=input('enter order:'); 
n=input('enter number of data points:');
x=[1 2 3 4 5 6];
y=b(0)+b(1)*sin(x)+b(2)*sin(x).^2;
x_l_mat=[];
y_l_mat=[];
x_l_mat=[x_1_mat; x_1];
y_1_mat=[y_1_mat; y_l];
if (n<(m+1))
    disp('regression is impossible');
else
for i=1:m+1
    for j=1:i
        k=i+j-2;
        sum=0;
        for l=1:n
            sum=sum+(x_l).^k;
        end
        a_(i,j)=sum;
        a_(j,i)=sum;
    end
    sum=0;
    for l=1:n
        sum=sum+y_l.x_l^(i-1);
    end
    a_(i,m+2)=sum;
end
end

[Rik]

Have a read here and here. It will greatly improve your chances of getting an answer.

[John D'Errico]

I reformatted the question to be readable.

[Abi sek]

Thanks john