I accidentally encountered a problem when adding a polynomial trendline to a simple scatter chart of some test data.
I can adjust the polynomial "order" from linear (1st order) all the way up to 6th order. I can see the preview of the trendline is changing as I increment the order number. But accepting my desired selection of 6th order, the trendline is indeed 6th order but the displayed equation is only 3rd order.
The same problem occurs in PM2024 and NX Beta. I haven't tried it in earlier versions, but I am fairly sure it used to work correctly for higher order polynomial trendlines.
To make sure I'm doing it correctly, I opened the same file in Excel and the polynomial is correctly displayed.
In PlanMaker NX Beta (or indeed PM 2024), if you right-click on the trendline and select trendline properties, you can see that 6th order has been set correctly.
Can you reproduce it?
Thank you!
Jez
Trendline Polynomial won't go above 3rd Order
Trendline Polynomial won't go above 3rd Order
- Attachments
-
- Polynomial shown to 3rd order only :(
-
- Polynomial correctly shown to 6th order
-
- test-200mA.xlsx
- Trendline polynomial
- (12.65 KiB) Downloaded 42 times
Re: Trendline Polynomial won't go above 3rd Order
Thank you for the detailed report and the test file. I've been able to reproduce the issue and have forwarded it to the team for further investigation.
Re: Trendline Polynomial won't go above 3rd Order
That was a very fast reply, thank you!
I'm very (VERY) impressed by Softmaker and it's my absolute preferred set of Office tools and has been since I discovered you in 2008. I'm glad we have this community and connection with the developers that can look into issues. You wouldn't get that from "you know who".
I'm very (VERY) impressed by Softmaker and it's my absolute preferred set of Office tools and has been since I discovered you in 2008. I'm glad we have this community and connection with the developers that can look into issues. You wouldn't get that from "you know who".
Re: Trendline Polynomial won't go above 3rd Order
Thank you very much for your appreciation and kind words. We have analyzed this issue and determined that it is not a bug, but rather the intended design.
PM truncates coefficients that are close to zero. In the Excel formula, the leading coefficients are −7.6×10⁻²⁴, 1.4×10⁻¹⁸, and −9.6×10⁻¹⁴. This indicates that the curve can only be fitted to a third‑order polynomial with reasonable accuracy.
Even the coefficient for the third order is 2.8×10⁻⁹, so a second‑order polynomial would already be acceptable. Unless extremely precise measuring instruments are used, coefficients smaller than 1×10⁻⁸ generally reflect data jitter rather than meaningful physical behavior.
PM truncates coefficients that are close to zero. In the Excel formula, the leading coefficients are −7.6×10⁻²⁴, 1.4×10⁻¹⁸, and −9.6×10⁻¹⁴. This indicates that the curve can only be fitted to a third‑order polynomial with reasonable accuracy.
Even the coefficient for the third order is 2.8×10⁻⁹, so a second‑order polynomial would already be acceptable. Unless extremely precise measuring instruments are used, coefficients smaller than 1×10⁻⁸ generally reflect data jitter rather than meaningful physical behavior.