Comparison between Matlab and Igor

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Hi,

I am calculating the second derivative of a particular data range regarding Raman spectra both with igor and matlab....I noticed that the amplitude is higher in Matlab with respect to igor.....it is also likely that the position of a peak revealed in the second derivative has 1 wavenumber difference between matlab and igor....this seems a bit strange to me since its the same data set. Any suggestions?

Thnaks,

Konstantinos
Konstantinos Chatzipanagis wrote:
Hi,

I am calculating the second derivative of a particular data range regarding Raman spectra both with igor and matlab....I noticed that the amplitude is higher in Matlab with respect to igor.....it is also likely that the position of a peak revealed in the second derivative has 1 wavenumber difference between matlab and igor....this seems a bit strange to me since its the same data set. Any suggestions?

Thnaks,

Konstantinos

Graph2.jpg (23.48 KB)

February 27, 2015 at 06:19 pm - Permalink

Igor has 3 different kinds of differentiation algorithms. If you want agreement, choose the algorithm that Matlab also uses.

--Jim Prouty
Software Engineer, WaveMetrics, Inc.

February 27, 2015 at 08:29 pm - Permalink

Hi,

Thanks for that......However, how can i choose between algorithms? I am basically using the differentiate option given and just do it.....How is it possible to choose between algorithms?

Regards

February 28, 2015 at 05:20 am - Permalink

Hi,

i found out how to do it....however, using backward or forward differences solves the problem partly.....now the second derivatives seem a lot more similar but there is still a problem.....using matlab i get maximum negative values up to -3 in the second derivative, while with igor pro up to -2.....i am trying to understand why is that.

February 28, 2015 at 07:17 am - Permalink

Note that the Differentiate operation, if you don't use the /X flag, takes the source wave's X scaling into account. For example:
Make jack=sin(x/8)
Differentiate jack /D=dif1
SetScale/P x, 0, .1, jack
Differentiate jack /D=dif2
Display dif1, dif2


For information on X scaling, execute:
DisplayHelpTopic "The Waveform Model of Data"

February 28, 2015 at 01:40 pm - Permalink