Can't quite figure out why my syms is giving me an error

% Define the function in symbolic form:
syms x
f = exp(-0.5*x)*(4-x)-2 ;
% Differentiate f(x) in x:
Df = diff(f,x) ;
% Convert f and Df to function handle:
f = matlabFunction(f) ;
Df = matlabFunction(Df) ;
% Define initial guess:
Xest = 5 ;
fprintf('Initial guess = %f\n', Xest)

Initial guess = 5.000000

% Run a for loop for 10 iterations:
for i = 1:10
    % Call the function for next approximation:
    Xest = NewtonSol(f, Df, Xest);
    fprintf('i = %d,  Xest = %f\n', i, Xest)
end

i = 1,  Xest = -45.729976
i = 2,  Xest = -43.807300
i = 3,  Xest = -41.887610
i = 4,  Xest = -39.971139
i = 5,  Xest = -38.058150
i = 6,  Xest = -36.148939
i = 7,  Xest = -34.243841
i = 8,  Xest = -32.343235
i = 9,  Xest = -30.447556
i = 10,  Xest = -28.557302

function Xs = NewtonSol(Fun, FunDer, Xest)
% Newton-Raphson formula 
Xs = Xest - Fun(Xest)/FunDer(Xest) ;
end

Output

I should be getting this as an output

Initial guess = 5.000000 i = 1, Xest = -45.729976 i = 2, Xest = -43.807300 i = 3, Xest = -41.887610 i = 4, Xest = -39.971139 i = 5, Xest = -38.058150 i = 6, Xest = -36.148939 i = 7, Xest = -34.243841 i = 8, Xest = -32.343235 i = 9, Xest = -30.447556 i = 10, Xest = -28.557302

but for some reason syms has an error message

Answer 1

[Dyuman Joshi]

The error is not with the symbolic part of your code, but how your code is arranged/structured.

If any function(s) is(are) defined in a script file, it(they) must be defined at the end of the file, after all the script code.

Your code works after making that change (see above).