How to get a trendline plot in LabVIEW like Excel

[labviewman]

I have searched the support pages in NI for this but couldn't find an adequate answer on how to plot the same trendline that Excel plots w/o using Excel.  I have tried the curve fitting functions in LabVIEW, but nothing comes close to the Excel trendline plot.

I submitted this question before under support request #7202957, but I quit my job before it was resolved.

Any ideas?

Thanks,

Todd

[smercurio_fc]

A trendline is basically a curve-fit function, so perhaps you're not using the right parameters for the curve-fit function. Can you post your data, and perhaps a screenshot of what the Excel graph looks like. If you have an Excel workbook with the data and the graph, that would be great as well.

[labviewman]

Here is a sample Excel spreadsheet with the data and trendline plot.

Any help would be very much appreciated!

Thanks,

Todd

[labviewman]

Hmm, with a different dataset I tried a month ago the express curve-fit plot (while configuring the express vi) never looked good, but with this dataset, it looks good, but the plot of evaluating the data via poly-eval is wrong.  Must be something simple I am doing wrong (see LV 8.5.1 attachment).

[smercurio_fc]

Using the data from your Excel spreadsheet, this is what I get from the curve-fit functions:

Seems like a pretty-good fit to me. I'm not sure what you're trying to do with the polynomial evaluation stuff, though.


Message Edited by smercurio_fc on 07-30-2008 09:21 AM

[labviewman]

I was only looking at the polynomial coefficients...didn't even think of checking the other outputs of the the poly-fit vi.  Thanks for pointing out the obvious to a 13 year LabVIEW veteran (mostly communications using RS232, TCP, ISO-9141, CAN, etc)!

Strange, why doesn't using the poly-coefficients (i.e. f(x)=a0+a1*x+a2*x^2+a3*x^3+a4*x^4+a5*x^5) create the same result?

[smercurio_fc]

That's because in your code you were feeding the Y values to the Polynomial Evaluation function. That's why I said I didn't understand what you were trying to do with that function.

[labviewman]

It figures...a simple (dumb) mistake was my problem all along!  Thank you for your help!

[FBro]

This is an old thread but today I was struggling in plotting the next periods of a trendline like in Excel. So here is an example I did that could help someone else in the future.