how to solve tan(x)-tanh(x)=0

So I followed the exact directions on this book called Numerical Methods for Engineers and Scientists Using MATLAB and used this code:

 >> fun=inline('tan(x)-tanh(x)','x');
 >> x=linspace(-2,2,100);
 >> I=find(sign(f(2:end))-sign(f(1:end-1)));
 >> f=fun(x);
 >> for n=1:length(I)
    r(n)=fzero(fun, x({I(n) I(n)+1}));
 end

but then, for some reasons, MATLAB told me that the 'subsindex' was not defined for the 'cells' value, and then when I proceeded anyways by typing r, it told me that r, for some reasons was not defined. What did I do wrong?

Answer 1

[Star Strider]

The code needs updating:

fun = @(x) tan(x)-tanh(x);
x=linspace(-2,2,100);
f=fun(x);
I=find(sign(f(2:end))-sign(f(1:end-1)));
for n=1:length(I)
    r(n)=fzero(fun, x([I(n), I(n)+1]));
end

I replaced the inline call with an anonymous function, and created a variable range with ‘I(n)’. It now works.

[Semin Seo]

Thanks! but I just don't understand why the value in the middle doesn't say 0 instead of -5.821731985378165e-1

[Semin Seo]

never mind, I fixed that problem by setting the parameters just a bit wider

[Star Strider]

My pleasure!

You chose the correct approach with respect to your solution.

Answer 2

[Honglei Chen]

Try

fzero(@(x)tan(x)-tanh(x),-2)

This uses anonymous function instead.

HTH