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tqzhang@ja
Japan
2 Posts |
 Posted - 11/08/2003 : 11:02:08 AM
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Once I heard that Origin can do global fitting, so I want to know how? Thanks a lot.
By "global fitting", I mean a set of datasets share a common set of paraments. For example, there are 7 dataset of exponential decays, in form of "Ai+Bi*exp(-(t-t0)/tao))", i=1,2,3..7. Now I want to fit all the decays with same "tao" simultaneously. How to do this? And further, if I want to associate the "Bi"s of the decays, say I want them to meet a Gaussian form, Bi=C*exp(-(i-i0)^2/w^2), how to impose this condition in the fittings?
Edited by - tqzhang@ja on 11/08/2003 11:12:10 AM |
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Mike Buess
USA
3037 Posts |
Posted - 11/08/2003 : 12:15:25 PM
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How to do this?
1> Open the Advanced Fitting tool and select or write your function.
2> Select Action->Dataset and pick the dependent and independent datasets for the first curve.
3> Check Fit Multiple Datasets at the bottom.
4> Click the Add Data button and select dependent/independent datasets for the second curve. Repeat for additional curves.
5> Double-click on tao in the Parameter Sharing list at the left to share it with all curves.
6> Select Action->Fit and initialize all parameters. Note that shared parameters such as tao are only listed once. Non-shared parameters are repeated for each curve (A1, A2, ...) so the subscript i (Ai, Bi) in is not needed in your equation.
How to impose this condition?
I'm not sure if this is the best way, but I'd use the explicit expression for Bi in the fitting function...
A + C*exp(-(i-i0)^2/w^2)*exp(-(t-t0)/tao))
C, i0 and w can be parameters or constants. If you choose to make them constants then enter their values on the Parameter Initialization tab (second button from right). i must be a parameter but it won't be varied. On the Parameter Initialization tab set the value of i for each curve (1, 2, 3, ...) and uncheck the Vary? box at the right.
You may be able to do all of this by script using the nlsf object. However, I haven't done much scripted fitting so someone else will have to tell you how.
Hope this helps.
Mike Buess
Origin WebRing Member
Edited by - Mike Buess on 11/08/2003 12:17:27 PM |
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how to do global fitting with Origin7?