How Fit with a cubic polynomial

Share icon

Hello everyone,
I would make a fitting of my curve, to flatten my curve.
My tutor suggested I make a fit with a cubic polynomial.
So, I selected my curve (in blue) and then right click Analysis - Quick Fit - Poly - 3; so I got the red curve.
Now I should steal this polynomial curve to flatten my curve, as I do? Screen Shot 2016-01-19 at 11.46.00.png (103.11 KB)
It sounds like you want to use the fit curve. In the current data folder there will be a wave called "fit_wcube". This is what you want.

The data folder can be viewed using the data browser. Select the Data Menu and then the Data Browser item.

January 19, 2016 at 05:56 am - Permalink

I think perhaps you want the data set that results from subtracting the fit curve from your data, right? If so, find in the History window the command that was generated by Quick Fit. It will look something like this:
CurveFit/M=2/W=0 poly 3, junk/D

If you click on that line, Igor will select the entire command. Now press Enter and Igor will copy it to the command line. Now click at the end and add a /R flag to the end, and press Enter again. The fit will be repeated, but this time will generate a new wave with "Res_" at the start of the name. That wave will contain the residuals, which is simply what you get when you subtract the fit from the original data.

John Weeks
WaveMetrics, Inc.
support@wavemetrics.com

January 19, 2016 at 10:36 am - Permalink

johnweeks wrote:
I think perhaps you want the data set that results from subtracting the fit curve from your data, right? If so, find in the History window the command that was generated by Quick Fit. It will look something like this:
CurveFit/M=2/W=0 poly 3, junk/D

If you click on that line, Igor will select the entire command. Now press Enter and Igor will copy it to the command line. Now click at the end and add a /R flag to the end, and press Enter again. The fit will be repeated, but this time will generate a new wave with "Res_" at the start of the name. That wave will contain the residuals, which is simply what you get when you subtract the fit from the original data.

John Weeks
WaveMetrics, Inc.
support@wavemetrics.com


Perfect, thank you so much should be those who would like to get , tomorrow submit graphs to my tutor and let you know ! Thanks so much!!!

January 19, 2016 at 01:33 pm - Permalink

Small remark: "Poly 3" fits with a polynom comprising three coefficients: k0+k1*x+k2*x^2
For a cubic fit you will need to use "Poly 4".
HJ

January 20, 2016 at 01:47 am - Permalink


Thanks you johnweeks, so it is perfect!!!



HJDrescher wrote:
Small remark: "Poly 3" fits with a polynom comprising three coefficients: k0+k1*x+k2*x^2
For a cubic fit you will need to use "Poly 4".
HJ


Also thanks for the suggestion to use "Poly 4" .


Now I also " isolate " the "fitting Graph".

I have to make other , then how can I combine them into one graph ?

January 20, 2016 at 06:04 am - Permalink

There should be waves starting with "fit_" in the data browser (the other part is the original wave name, e.g., data1 & data2).
display fit_data1, fit_data2
would display both fits in one window.
display fit_data1
appendtograph fit_data2

is an alternate version to add more traces.
Also, please have a look on the documentation of "display" and "appendtograph".
HJ

January 20, 2016 at 07:19 am - Permalink

HJDrescher wrote:
There should be waves starting with "fit_" in the data browser (the other part is the original wave name, e.g., data1 & data2).
display fit_data1, fit_data2
would display both fits in one window.
display fit_data1
appendtograph fit_data2

is an alternate version to add more traces.
Also, please have a look on the documentation of "display" and "appendtograph".
HJ


Ok, i try it, but it is not what I want.

I try with:

display Res_data1 vs time1
appendtograph Res_data2 vs time1

It's probably works

January 20, 2016 at 07:26 am - Permalink