one equation with one unknown variable

Hello,

I want to solve equation with one unknown variable (x).

Matlab code: Editor: function y = f(x)

y=(18/5)*((1-x)^(-1/6))-(162/29)*((1-x)^(-1/9));

Command window: x=fzero(@f,[0,1])

(x should be between 0 and 1)

And the error is: ??? Error using ==> fzero at 283 The function values at the interval endpoints must differ in sign.

What should I do to solve that equation correctly?

And help will be appreciated.

Answer 1

[Konstantinos Sofos]

Hi,

fzero checks that fun(x0(1)) and fun(x0(2)) have opposite signs, and errors if they do not. In you example the upper bound gives NaN

>> y=@(x)(18/5)*((1-x)^(-1/6))-(162/29)*((1-x)^(-1/9))

y = 

      @(x)(18/5)*((1-x)^(-1/6))-(162/29)*((1-x)^(-1/9))

>> y(0)

ans =

     -1.9862

>> y(1)

ans =

     NaN

Does this help you how to continue program with fzero error ?

Regards

Answer 2

[Roger Stafford]

I would recommend that you alter the interval:

   x=fzero(@f,[0,.999999]);

There is an easier way of solving it. Substitute t = (1-x)^(-1/18) and get an equation in t, which can be easily solved. From that you can get back to a solution for x.

[John D'Errico]

As Roger points out, the transformation is the correct way to do it - a slam dunk solution.

[Lojzika]

Thank you for your answer

[John D'Errico]

I am confused as to why you would accept the other answer as this is so clearly the correct one. Oh well, Roger's answer got my vote.

[Konstantinos Sofos]

@John D'Errico could you explain us also why my answer is not valid or the correct one? Do we have any competition here or shall we try to provide our view? I am sorry for your comment...