无法从 sym 转换为 logical

syms x;
f=3*x^2-exp(x);
g=diff(f);
r=solve(f,x);
h=diff(g);
r
rs=r-6*r-exp(r)/6-exp(r);
rs
max=2000;
err=0.5*10^(-7)
abs(r-rs)
err
for i=1:max
if abs(r-rs)<err;
break
else
r=rs;
rs=r-6*r-exp(r)/6-exp(r);
end
end;
rs