Convert measured data into equation
Convert measured data into equation
(OP)
Hi, i have some measured data, that when you plot them will result in a 3rd order polynomium.
Anyone know of a way to calculate the 3rd order coefficients???
Anyone know of a way to calculate the 3rd order coefficients???





RE: Convert measured data into equation
TTFN
RE: Convert measured data into equation
RE: Convert measured data into equation
TTFN
RE: Convert measured data into equation
X = 1 0.1 0.1^2 0.1^3
1 1.1 1.1^2 1.1^3
1 2.1 2.1^2 2.1^3
1 3.1 3.1^2 3.1^3
The inver X using excel or inv in MATLAB or 1 / X in the TNT (Template Numerical Toolkit) available for free on the net for C++.
if your data is
y = 5.3 6.3 7.3 8.3
Then you would multiply y as a column vector by inv(x) to get your coefficients.
c = y * X^-1
This is only OK for "good" data with less than 10 points. If you have more points you should use a numerically better solution as suggested by
IRstuff
as in Numerical Recipes
or the TNT library
or the MATLAB backslash or QR functions. You would also want to augment them as explained in the literature.
RE: Convert measured data into equation
RE: Convert measured data into equation
Format Data Series
Custom.
You will get a line through the points.R-click on the line and you will get a form Add Trendline.
Under Type choose Polynomial, Order 3;
under Options choose Display Equation On Chart
and you'll get it!
If you want a differently formated result then right clickt he result, choose FormatData Labels and then choose one of the available formats (number, scientific..).
You can copy the result into a cell on a sheet but however the result is written as a string of chracters so you need some work to separate constants of the polynomial as individual values in particular cells.
m777182