Functions at the prompt

[AME55]

Hi...

I am writing a code for Newton-Raphson Method. I wrote three M-Files:
1)Function m-file

function f = f(x)
f = input('Enter Your Function Interms of x ');

2)Derevitive m-file

function df = df(x)
df = input('Enter The Derivitive Of The Above Function Interms of x ');


3)Script m-file (was done with help of online resources)

a = input('Enter Your Initial Guess ');
Tolerance = input('Enter The Desired Tolerance ');
error = 1;
n = 0;

while error > tol
x = a - f(a)/df(a);
error = abs(x-a);
n = n+1;
if n > 25
error('Excessive iteration and no convergence.');
end
a = x;
end


disp('Tolerance (s)')
disp(Tolerance)
disp('Number of iterations')
disp
disp('Root of function')
disp(x)



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The Script File works just fine, especially the part of having the user to enter his/her values. But as you can see for other M-Files, I want also the user to enter his/her function as well. But the method is simply not working.

I want a way in which the user can input the functions manually. Is there such a way?

Thank you guys.