Hi all, I am trying to write a Fixed Point Iteration program but when I enter in the command line it kept giving me an error message. Can you please look over my program and tell me what might have gone wrong? Thank you very much!

First, I defined a function in a new M-File: 

function y=FUN3(x)
y=5/(sin(x)*exp(-x./2));

Then, I opened up another M-File and wrote the program:

function Xs = FixedIterationRoot3(FUN3,Xest,imax)
syms x FUN3 FunDer3
Xi(1)=Xest;
FUN3=5/(sin(x)*exp(-x./2));
FunDer3 = diff(FUN3)    % To find g'(x)

if abs(subs(FunDer3,x,Xest))>=1  % to check if g'(x) diverges
   return;
   fprintf('not valid')
end

for i=2:imax
    Xi(i)=feval(FUN3,Xest);
    Xest=Xi(i);
    Xs=Xi;
end



When I enter in the command line:
>> xSolutions=FixedIterationRoot3('FUN3',-3,10)

it gave me error message: 
syms x FUN3 FunDer3

??? Output argument "Xs" (and maybe others) not assigned during call
to
"C:\Users\Jane\Documents\MATLAB\FixedIterationRoot3.m>FixedIterationRoot3".