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Topic: Zero Crossing
Replies: 1   Last Post: Jan 28, 2013 2:14 PM

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Derek Goring

Posts: 3,922
Registered: 12/7/04
Re: Zero Crossing
Posted: Jan 28, 2013 2:14 PM
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On Tuesday, January 29, 2013 5:08:08 AM UTC+13, Pete wrote:
> Hi,
> I'm very new to matlab and need to calculate individual wave crest heights from ocean wave height data. So far i have selected the column of data that i want to look at and cut the data size down slightly. I think the next step is to use the sign function to get 1's, -1's and 0's from the data. Here's what I have so far:
> s=load('sample.txt');
> e1=s(:,9);
> eta1=e1(6000:end);
> sgn=sign(e1);
> ff=find(sgn==0);
> Does anyone know what i have to do next? Any help would be great!

No, you need to find the points where the signs change:
Now, indx contains the locations of the zero crossings (upward and downward) as shown here:

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