Instantaneous frequency not plotting correctly in Matlab

Posted by user2951069 on Stack Overflow See other posts from Stack Overflow or by user2951069
Published on 2013-11-06T03:51:45Z Indexed on 2013/11/06 3:53 UTC
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matlab

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plot

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frequency

I'm trying to convert square wave data to instantaneous frequency and plot against time. It works correctly for one data set, but three others are plotting as shown in the image: http://i.imgur.com/iuL648o.png

Time is linear, so it shouldn't be plotting like that. Anyone have any ideas as to what's going on? I'm using the following code:

ddiff = diff(flow(:,1));
locations = find(ddiff(1:end-1,1)>0.1 & ddiff(2:end,1) <=0.1);
for z = 2:length(locations)
    inst_freq(z-1) = 1/(time(locations(z))-time(locations(z-1)));
    freq_time(z-1) = time(locations(z));
end
plot(freq_time,inst_freq)

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