Integral

[thopaParticipant]

Hello,

I have 3 columns. Column “a” includes values from 1.5 to 6 with 45 entries. These entries are repeated. Column “b” has values and “c” has more values than “b”. More precisely, “c” has values for a=1.5, “b” has no values for a=1.5. Every value else should be identical in “b” and “c”.

 

If I use a global variable to calculate the integral between “a” and “b” it is greater than the integral between “a” and “c”. Maybe I’m missing something basic here. Why could the integral between “a” and “b” be greater than the integral between “a” and “c” if “c” should be the same as “b” but with a few additional values >0?

 

Thank you in advance!

 

[thopaParticipant]

Okay, it just came to my mind that having no number in “b” instead of 0 could probably change the integral. Is this the problem here?

[dgteamModerator]

Yes, the missing value in b will make a difference, as the integral here is cumulative across the enter set of data.  To understand what is happening, you might to try using a Plot action column to compare the results.

Do you just want to integrate what looks like a peak from x= 2.7 to  x= 3.5?  You could mask out the first set of rows with a Mask column, and then integrate the masked data.  Just make sure to include the zeros around the peak.

Also, in our beta version, the Fit command has a Fit function option called ‘Peaks’, that might be useful.  That can be used to find multiple peaks.

 

 

[dgteamModerator]

Here is an example with the Plot action column, using similar data, where the last entry will match the cumulative integral from the expression variable.

If you plot the result, you can see the impact of the first points.

Hope this helps!

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