zero crossing determination in octave?

[Jack Crenshaw]

Carlo de Falco wrote:
>
> On 05/dic/08, at 20:07, J. Patrick Bedell wrote:
>
>> Hello,
>>  Is there an octave function to compute (possibly using
>> interpolation) the points at which a given waveform crosses the x-axis
>> (or a specified threshold value)?
>>  Thanks!
>>
>>  Patrick
>
> Don't know whether this already exists but it seems to me it's trivial 
> to implement,
> see the attachment...
> c.
>
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Um ... I think Patrick was looking for a function that would iterate on 
the solution. In Matlab, that's fzero.  Your function is only a linear 
approximation, which might be Ok if the data array is dense, but 
otherwise, NG.

Jack