How linear regression of -20 dB on the graph?

[Daikataro]

Like Ravensfan said, you most likely have your data as a 1D or 2D array, just use the "array subset" function at the graphic points you're interested in, send that as an auto-indexed tunnel to a for loop with the regression function and have the result output as an auto-indexed tunnel too.

[G.Orkia]

Ok thank you very much for your reply, I try to do this right away !!

G.Orkia

[G.Orkia]

There is something I do not understand how I can select the points that interested me from a graph?

G.Orkia

[RavensFan]

I don't know.  As a person, how do you know what points interest you on the graph?

Once you know that, you can figure out how to program it.

If you are looking for something where the points have an X-value between 10 and 20, for instance, search the array for the first point that is 10 or greater, then the first point that is greater than 20.  Now you'll have 2 indices.  I1 and I2.  Use array subset where you start at I1 and the length is (I2-I1).  Do the regression on that subarray.

If there is some other criteria that determines what points are interesting and which aren't, then you'll have to work out a different method of selecting points out of the array.

[G.Orkia]

We want to study the 5dB points below the maximum, so make a regression to a fall of -20 dB and -30 dB. The problem is precisely that the values always change according to the try that we do, so I can not say ps at what points.

[RavensFan]

Okay.  So where is the problem?

What I proposed is how you analyze it once you've got the data.  Find the maximum.  Subtract 5 dB.  Use that as your criteria when you search the array.

[billko]

Pleas note that these aren't even LabVIEW questions so far...

[G.Orkia]

Hi 

I have the impression that this is telement easy, but I really galley understand how to select an maximum point from a graph therefore a table, is there a function capable of that. For me the best way is to write a matrix but I'm really bad.

G.Orkia

[GerdW]

Hi G.,

THINK DATAFLOW!

You don't select a "maximum from a graph" as a graph is an indicator (data sink)!

You should have an array as data source - that's the place (data source!) you have to look for your maximum!

And well, there is an ArrayMinMax function in the array functions palette…

For me the best way is to write a matrix but I'm really bad.

No, you don't need matrizes for this. (They are a special datatype in LabVIEW!)

All you need are arrays, one with Y values, one with corresponding X values…