Untitled Document
Christoph Frommen,
I have been able to successfully fit your data. The way I did it was as follows:
- Create a new Y column next to the Y column with the original data and fill it with the negative of the original Y values. To do so, click on the new column and select Column:Set Column Values. Enter the line -(col(b)) (assuming the original data is held in a column named 'b') and click the Do It button.
- Plot these newly calculated values as a line plot. Notice that the peaks display in the positive direction. This is important since the initial settings in the fitter do not work too well with negative peaks.
- Selected Analysis:Fit Multi- peaks:Lorentzian to fit the data. This provides a quick way to get a decent fit, but usually requires some parameter value adjustment to get the fit just right.
- To get the fit just right, select Analysis:Nonlinear Curve Fit and alter the parameter values corresponding to the centers of the peaks. These would be the parameters called (xc1, ..., xc6). If you are unsure how to alter them, try using the Data Reader tool on the Tools toolbox to estimate better center values for your peaks.
- Fix xc1, ..., xc6 once you are satisfied with their positions. To do so, uncheck the Vary? check boxes next to each.
- Perform several more iterations until the fit looks good. To do so, click the 10 Iter. button.
- Go back to the worksheet and plot your original Y data.
- Go back to the fitter and change the Y dataset assignment to your original Y dataset. To do so, select Action:Fit. If you do not see any menus in the fitter, you are not in the advanced mode. To get there, click the More button. Once you have selected Action:Fit, click on the Y Dep line in the Variables Datasets Fitting Range interface, select the original Y dataset from the Available Datasets list box, and click the Assign button.
- Select Action:Fit and add negative signs in front of all the amplitude parameter values (A1, A2, ..., A6).
- Click the 10 Iter. button to perform some iterations. You should see a pretty good fit. The red fit line is the actual fit line and the green fit lines are the individual fits of each of the peaks. These can be removed by going into the Layer Properties (double-click on the layer 1 icon in the top left corner of the graph window) and moving them out of the Layer Contents.
This may sound complicated, but it actually isn't that difficult. If I have misunderstood your question, or you have trouble following the steps, feel free to contact Microcal Technical Support for further assistance. You can either call the following number:
(800)969-7720 (press option 2)
or send an e-mail by clicking on the link above. Please be sure to provide the following information:
- your serial number,
- the operating system name,
- the dataset you provide in the Forum, and
- a step-by-step description of how you perform the fit in Origin (from start to finish).
Thank you for your interest in Origin.
Sincerely,
Ryan Toomey
Microcal Software, Inc.
[This message has been edited by rtoomey (edited 03-19-99).]
Problems with Fitting Multiple Lorentzians
Posted - 03/16/1999 : 10:04:00 PM
