Re: Zero crossing

[James Sherman Jr.]

On Mon, Jan 21, 2013 at 3:13 PM, expikx <address@hidden> wrote:
> hey all,
>
> i´ve got some problems with the determination of zero points of a fitted
> function.
>
> this is what i have done:
>
> 1) data input with A=load("-ascii", "file.csv")
>
> 2) naming my data with x = A(:,1) and y = A(:,2)
>
> 3) fitting with P=polyfit(x,y,4)
>
> 5) S=polyval(P,x) to get the fitting polynome (am i right?)
>
> for my next step in need the zero crossing point of my fitted function. By
> typing roots(S) i just get imaginary solutions, but there are real
> solutions! I also tried the command fzero and nothing happens :-(
>
> may you help me?
>
> thx a lot
>
> cheers,
> expikx
>
>
>
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Hi expikx,

You should pass the vector of the polynomial coefficients to the roots
function, not the evaluation of the polynomial at those points.

Hope this helps,

James Sherman