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I have a (rough) known period sine wave coming in, held in an array, with superimposed noise. I need to find and count the maxima and minima (in C). Any suggestions or algorithms? The signal has already been received and buffered, so not real time.

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If you have the entire signal, you can then run a Lowess smoothing. This algorithm is statistically robust and provides locally acceptable smoothing. Outliers will be tolerated as well. After smoothing your signal in that way, you might apply a derivative based (or even derivative free) peak detection in order to obtain the signal peaks. These will be your local minima/maxima.

You could use MATLAB or R and port smoothing algorithms to C, they are pretty straightforward and open source:

http://www.mathworks.com/help/curvefit/smooth.html

And here are your options in C:

1) https://code.google.com/p/variationtoolkit/ for Lowess/Loess. 2) For peak detection, there are many tools available in C, one of them being:

https://github.com/xuphys/peakdetect

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