How do I compute the second derivative of a one-dimensional array?

[fresh_42]

Yeah, I am going to remove it. Sorry, I never code a function to take a derivative of a graph before and I could not find any YouTube videos on how to do it by hand.

See my post #27. It is an instruction.

 

[berkeman]

So Basically to take the first derivative, I am going to go through the array and subtract index + 1 from index.
So:
double value = spectrumData[i + 1] - spectrumData;

You need to get your units right in your derivative calculations (both for the numerator and denominator). The units for the numerator look to be "counts" right? And for the denominator, you have bins separated by some delta-energy in keV? So the units of the first derivative would be delta-counts per delta keV?

 

[berkeman]

So the units of the first derivative would be delta-counts per delta keV?

It looks like the horizontal bins are spaced linearly? What is the increment in delta-keV per bin? It looks like a small fraction of a keV delta per bin?

 

[btb4198]

You need to get your units right in your derivative calculations (both for the numerator and denominator). The units for the numerator look to be "counts" right? And for the denominator, you have bins separated by some delta-energy in keV? So the units of the first derivative would be delta-counts per delta keV?

Yes, that is all correct.

 

[btb4198]

It looks like the horizontal bins are spaced linearly? What is the increment in delta-keV per bin? It looks like a small fraction of a keV delta per bin?

From this picture is looks like the bins increase by one .

 

[btb4198]

Another question, if I were to place this Spectrum into an FFT would my sampling rate(fs) be 1hz ?

 

[berkeman]

From this picture is looks like the bins increase by one .

One what? One eV? Could be -- please take care to always include units with the numbers. Thank you.

 

[Mark44]

From this picture is looks like the bins increase by one .

I don't think so. The increments along the horizontal axis (eV) increase by 2000 eV. Since you're attempting to find an approximation to the derivative, is your math background sufficient for you to understand what you're trying to do? That is, have you taken calculus sometime in the past?

 

[berkeman]

Another question, if I were to place this Spectrum into an FFT would my sampling rate(fs) be 1hz ?

No. You already have a plot of counts per fraction-of-an-eV. What domain do you want the FT to transform that into? You can't randomly do FFT processing on data and get meaningful information.

 

[Mark44]

You can't randomly do FFT processing on data and get meaningful information.

In short, GIGO...

 

[btb4198]

No. You already have a plot of counts per fraction-of-an-eV. What domain do you want the FT to transform that into? You can't randomly do FFT processing on data and get meaningful information.

In the example excel file, could you put that into an FFT? Or no ?
anyhow, The Output of the DPP is Very noise, so I wanted to filter out the noise.

 

[berkeman]

In the example excel file, could you put that into an FFT? Or no ?
anyhow, The Output of the DPP is Very noise, so I wanted to filter out the noise.

Your thread is now temporarily locked. I will send you a Private Message (PM) in a few minutes to try to salvage it.

 

[berkeman]

After the PM discussion with the OP, there is no reason to re-open this thread. Thanks everybody for trying to help the OP out.