have received a number of inquiries related to fitting with multiple
independent variables. Here are just a few:
have a set of data with two input variables (X1 and X2) and one
output variable (Y). I can graph this data but have not figured
out how to curve-fit it?"
I have 3 columns A(x1, x2,... x1000), B(x1, x2,....,x1000), and
C(x1, x2,....,x1000) and want to fit column C with A and B: C(x1,
x2,... x1000)=a*A(x1, x2,....,x1000)+b*B(x1, x2,....,x1000), how
can I use the NLSF to find coefficients a and b?"
Origin capable of fitting a 3D linear plane of best fit?"
If you are among
the many users who have been asking the same questions about Origin,
take a look at the following two examples to find some answers.
Example 1: Fitting Three Dimensional Data
This first example
describes the procedure for fitting matrix data to a fitting function
containing multiple independent variables. Specifically, random
data describing a three dimensional gaussian peak will be fitted
in order to find the amplitude of the peak, and the centroids and
widths of the peak along the x and y dimensions.
Download the Project
To begin, download
3DFit.EXE from one of the following locations:
3dfit.exe which contains 3DFIT.OPJ:
Save the *.EXE
to a location of your choosing or accept the default. Next, open
Windows Explorer and navigate to where you have saved 3dfit.exe.
Double-click on the file to extract the file called 3DFIT.OPJ.
Specify the location where you wish the file to be saved or accept
the default and click Unzip. Finally, launch Origin and open the
Once the project
is opened you should find that 3DFIT.OPJ contains a matrix
window called RawData. RawData contains the experimental values
of the three dimensional gaussian data. The project also contains
a 3D Color Map Surface graph of RawData called RawDataPlot.
At the end of Example 1 RawDataPlot will compared to a 3D Color
Map Surface graph of the fitted data.
Setting Up the Worksheet
During any fit
using the nonlinear curve fitter Origin requires the data to be
presented in two dimensional form. This requirement is independent
of the number of dimensions (variables) that describe your data
(3 in our case - x, y and z). Since this is the case, RawData
must be converted
into a worksheet. Once this is done, the resultant Z column must
be changed to a Y column.
to Worksheet => Regular
To start, make
sure RawData is active and select Edit:Convert to Worksheet:XYZ
Columns. An intermediate dialog box called Convert to Matrix
Wksheet will come up asking you to specify how you would like
your data to be sorted (X Constant 1st or Y Constant 1st).
Click OK to accept the default (X Constant 1st). Your data
is converted into an Origin worksheet called Data1.
C(Z) to C(Y)
right-click on C(Z) and select Set As:Y. Alternatively,
click once on C(Z) and select Column:Set As Y from the Origin
menu bar or double-click on the column title to bring up the Worksheet
Column Format dialog box and set the Column Designation
drop-down list to Y. Click OK to close out of the dialog box if
you choose to use the last method mentioned here. The column designation
for column C is changed to (Y) and the conversion to two dimensional
form is complete.
You are now
ready to define
the fitting function.