Re: fzero tolerance issue ... and a related bug

[Jordi Gutiérrez Hermoso]

On 17 October 2012 15:52, Joza <address@hidden> wrote:
> function [zero iterations] = Mzero(X1, X2, Xtol, Max_its)
>
> [X, fval, INFO, OUTPUT ] = fzero( "FUN", [X1,X2], optimset("MaxIter",
> Max_its ) );
>
> zero = X;
> iterations = OUTPUT.iterations;
> **************************************************************************************************************
> "FUN" = abs(x-9.1)^4.5;
>
> X1 = 8.0
> X2 = 13.0

FUN is always nonnegative, so there is no valid bracketing except the
trivial bracketing [9.1, 9,1].  A valid bracketing [x1, x2] in such
that x1*x2 <= 0.

You should use a method based on minimisation instead of one based on
bracketing.

- Jordi G. .