I need help with this false position script

I'm not sure where the issue is. Note the percent notes below the script has some commands that need to copy and pasted into the command box.

function root= fp(func,xl,xu,es,max)

if func(xl)*func(xu)>0

error('input error')

end

if nargin<5

max=50;

end

if nargin<4

es=0.001;

end

iter=0;

xr=xl;

while(1)

xrold=xr;

xr=xu-func(xu)*(xl-xu)/(func(xl)-func(xu));

iter=iter+1;

if xr~=0

ea=abs((xr-xrold)/xr)*100;

end

test=func(xl)*func(xr);

if test<0

xu=xr;

elseif test>0

xl=xr;

else

ea=0;

end

if ea<=es||iter>=max

break

end

end

root=xr;

%Type the following commands below

%format long

%fx=@(x)-12-(21*x)+(18*x^2)-(2.75*x^3)

%fp(fx,-1,0,0.001)

Answer 1

[Stephan]

No idea what your problem is, code runs for me:

format long
fx=@(x)-12-(21*x)+(18*x^2)-(2.75*x^3)
a =sprintf('%.8f', fp(fx,-1,0,0.001))
function root= fp(func,xl,xu,es,max)
if func(xl)*func(xu)>0
  error('input error')
end
if nargin<5
  max=50;
end
if nargin<4
  es=0.001;
end
iter=0;
xr=xl;
while(1)
  xrold=xr;
  xr=xu-func(xu)*(xl-xu)/(func(xl)-func(xu));
  iter=iter+1;

    if xr~=0
    ea=abs((xr-xrold)/xr)*100;
    end

    test=func(xl)*func(xr);
    if test<0
        xu=xr;
    elseif test>0
        xl=xr;
    else
        ea=0;
        end
    if  ea<=es||iter>=max
        break
    end
    end
root=xr;
end