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

[James Sherman Jr.]

On Thu, Oct 18, 2012 at 1:46 PM, Joza <address@hidden> wrote:

So related to all that above, how does one find the root of a function that
is always positive, or zero, but never negative? For instance, an absolute
value:  f(x) = abs(x - 2)

This has root 2, but I can't give it an initial bracket [x1,x2] since
f(x2)*f(x2) >= 0.
Indeed, how could fzero even find an initial bracket?

So how can one solve such a simple equation with fzero?



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Since fzero depends on a change of sign, then I'd probably say for a function that is non-negative, you'd have to do some kind of preprocessing on that function.  You could try feeding the derivative of a function into fzero, thereby finding the local extrema, then checking whether the extrema are zeros.  In general, I believe finding zeros of those types of functions is better served using a gradient descent solution.

Hope this helps,

James Sherman