Problem with Newton-Rapshon code

So I have this simple code:

function y=divsin(fun,xo,tol)
dfun=diff(sym(fun));
f=subs(fun,xo);
df=subs(dfun,xo);
c=1;
while abs(f)>tol
    a=xo-f/df;
    f=subs(fun,a);
    df=subs(dfun,a);
    xo=a;
    c=c+1;
end
c
a

I need help to find out my mistake. This is what I get when I execute it:

divsin('x^2-2',1,0.0001)
Error using sym>convertChar (line 1459)
Character vectors and strings in the first argument can only specify a variable or
number. To evaluate character vectors and strings representing symbolic expressions, use
'str2sym'.

Error in sym>tomupad (line 1225)
        S = convertChar(x);

Error in sym (line 214)
                S.s = tomupad(x);

Error in divsin (line 3)
dfun=diff(sym(fun));

Answer 1

[Areej Varamban Kallan]

Hi Diego,

In your code, you are passing a character array to 'sym', this is not correct. Add the following line after function definition.

fun = evalin(symengine,fun);

Change the defintion of dfun to:

dfun = diff(fun);