Problem with Newton-Rapshon code

Question

Diego Sanchez 2019-2-6

0
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/443601-problem-with-newton-rapshon-code

编辑： Areej Varamban Kallan 2019-2-7

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));