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: t1=e1(1:end-1); t2=e1(2:end); tt=t1.*t2; indx=find(tt<0); Now, indx contains the locations of the zero crossings (upward and downward) as shown here: t=[0:length(e1)-1]'; plot(t,e1,'b-',t(indx),e1(indx),'rx')