Trying to find the error in my modified false position method code

I am getting this error (Index exceeds the number of array elements. Index must not exceed 1) for my code and unsure why. Any help would be appreciated.

clc;
clear all;
close all;

%Mini Project

%Modified False Position Method
syms f(x);
f(x)=(-4.868e-7)*(4*x^3)+(1.496e-4)*(3*x^2)+(-0.0094)*(2*x)+(-0.3324);

i=1;

xl(i)=150;
xu(i)=200;
iu(i)=0;
il(i)=0;

fu(i)=f(xu(i));
fl(i)=f(xl(i));
xr(i)=xu(i)-((fu(i)*(xl(i)-xu(i))/(fl(i)-fu(i))));
fr(i)=f(xr(i));

ea = zeros(1,i);

if f(xr(i))~=0
    while i<100
        i=i+1;
        if fl(i-1)*fr(i-1)<0
            xu(i)=xr(i-1);
            xl(i)=xl(i-1);
            iu(i)=iu(i-1);
            il(i)=il(i-1)+1;
            if il(i)>=2
                fl(i)=fl(i-1)/2;
                fu(i)=fr(i-1);
            end
        else
            xl(i)=xr(i-1);
            xu(i)=xu(i-1);
            il(i)=il(i-1);
            iu(i)=iu(i-1)+1;
            if iu(i)>=2
                fu(i)=fu(i-1)/2;
                fl(i)=fr(i-1);
            end
        end
        xr(i)=xu(i)-((fu(i)*(xl(i)-xu(i))/(fl(i)-fu(i))));
        fr(i)=f(xr(i));
            ea(i)=abs((xr(i)-xr(i-1))/xr(i))*100;
            if ea(i)<0.05
                break;
            end
    end
end

Index exceeds the number of array elements. Index must not exceed 1.

Error in indexing (line 962)
R_tilde = builtin('subsref',L_tilde,Idx);

figure(1)
plot(ea)
hold on
grid on
xlabel('Iteration')
ylabel('Percent Approximation Error')

y=-200:10:200;

figure(2)
hold on
grid on
box on
for i=1:1:length(y)
    plot(y,f(y),'LineWidth',2)
end

plot(xr,f(xr),'*','MarkerSize',10);
xlabel('Temperature (K)')
ylabel('Derivative of f(T)')
yline(0);

xr=double(xr);
r_mfpm=(-4.868e-7)*(xr^4)+(1.496e-4)*(xr^3)+(-0.0094)*(xr^2)+(-0.3324*xr)+14.55;   

et=abs((166.222229010761-xr)/-166.222229010761)*100;
         
 

[James Tursa]

To debug this, type the following at the command prompt:

dbstop if error

Then run your code. When the error occurs, the program will pause at the line causing the error with all variables intact. Then you can examine the variables on that line to figure out the cause of the error. In your case, some of the variables are scalars but you are using an index of 2, hence the error. Backtrack in your code to figure out why these variables are not the size you expected.

Answer 1

[Aman]

Hi Lily,

You are getting the below error from the below line:

xr(i)=xu(i)-((fu(i)*(xl(i)-xu(i))/(fl(i)-fu(i))));

Here "fl" and "fu" are 1x1 syms, and the code is trying to access the second index, due to which it is erroring out. Please reiterate your code once and make appropriate changes, like accessing the proper index or assigning the proper type to the "fl" and "fu.".

I hope this helps!

[Lily]

I'm confused on how I would fix the error.