About FindPeak

Read the documentation carefully:

Here FindPeak returns a minimum. Maybe you want:

to define a "peak" to be something larger than 0.

Thanks for your reply.

Attached file is my full data, while I use "FindPeak", only wave14 and wave33 return negative peak, but take wave0 as example, first peak isn't it should be minimum at row 4 or 5 for value -2.66 ?

FindPeak finds maxima unless you use the /N flag.

I loaded your second file into Igor 8 and then used FindPeak on several of the waves:

These all have found the obvious first positive peak.

Thanks for your reply.

I think I make some mistake while typing the wave name

Following is what I got with FinkPeak by Igor Pro 6.22A

*FindPeak wave13
  V_Flag= 0; V_PeakLoc= 2; V_PeakVal= -2.742; V_LeadingEdgeLoc= 2; 
  V_TrailingEdgeLoc= 2; V_PeakWidth= 0; 
*FindPeak wave32
  V_Flag= 0; V_PeakLoc= 3; V_PeakVal= -2.808; 
  V_LeadingEdgeLoc= 1.5; V_TrailingEdgeLoc= 3; V_PeakWidth= 1.5; 

It seems like a small 'drop in intensity', so to speak, at the beginning of this particular data confuses FindPeak (which looks in the derivate data). The solution here is to increase the box size for the sliding average or flat-out define a minimum level which needs to be crossed for a peak:

I don't know why, but these two approaches give slightly different results. See what works best for you.

Using Igor 6.37 i get the same result you get. I guess things have been improved over the last 2 1/2 years! You can get the same result I got if you upgrade.

I got it thanks for everything.

For people coming to this topic later, I'd like to note that nearly all data has noise that needs smoothing out before FindPeak's simple derivative algorithm works well.

That means either use FindPeaks on data you have already smoothed, or always use the /B=boxPointsToSmooth flag.

And /M=minLevel (thresholding) is usually a good idea.

These ideas are used in the simple automatic peak-finder implemented in the procedure file: