MATLAB: Number of elements error

errorMATLAB

p = [2 3 4 5 6 7 8 9 10];
L2 = zeros(size(p));
xchange = zeros(size(p));
f = @(x) (cos(2*x)).*(sin(x)-0.5*x.^2);
for j = 1:length(p)
    n = 2^(p(j));
    x = linspace(-3,3,n);
    dx = x(2)-x(1);
    L = 0;
    ff = [];
    for i = 3:(length(x)-2)
        ff = (-f(x(i+2))+6*f(x(i+1))-3*f(x(i))-2*f(x(i-1)))/(6*dx);
        %ff = (-1*x(i+2)+6*x(i+1)-3*x(i)-2*x(i-1))/(6*dx);
        L(i) = dx*((f(x(i))-ff)^2);
        L = L + L(i);
        
    end
    %ff(1:2) = ff(3);
    %ff(n-1:n) = ff(n-2);
    L2(j) = L.^0.5;
    xchange(j) = dx;
end
plot(log(xchange),log(L2))
hold on
Hi, can anyone help me with this. I have been spending hours to solve the error printed in the command window below;
"Unable to perform assignment because the left and right sides have a different number of
elements.
Error in Untitled2 (line 24)
L2(j) = L.^0.5;"

Best Answer

    for i = 3:(length(x)-2)
        ff(i) = (-1*x(i+2)+6*x(i+1)-3*x(i)-2*x(i-1))/(6*dx);
        
        L = L + dx*((f(x(i))-ff(i))^2);
        
    end
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