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phenning
USA
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 Posted - 09/14/2009 : 5:50:13 PM
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Origin Ver. 8.0 (Demo) SR6
Operating System: Vista 64 SP2
I'm trying to analyze fluorescence lifetime data using the method here:
http://wiki.originlab.com/~originla/howto/index.php?title=Tutorial:Fitting_With_Convolution
This method works for the sample data provided by Origin, but I'm having problems with my data. NLSF only returns the first 100 or so points out of 512 datapoints in the dataset. Also, the time axis appears to be stretched in the fitting window. And, when I look at the output data, the time values are resampled (1,5,10... vs 1,2,3...). Also, when I plot the convoluted response against the original time axis, the fit is quite good, except that the tail end of the curve (80% of the data) is absent. However, the residuals are calculated for all time values in the original data. The tail end has a lot of significance to the recovered lifetimes/parameters for fluorescence lifetime data.
I cropped the measured data to 512 points, then cropped the response function to 255 points, and finally cropped the response function to 233 datapoints. I've also tried this with simulated data using the convolution routine in Origin with my response function. In all cases, the result was the same as described above.
I also tried to perform convolution without the FFT using the code below, but the NLSF only performed 1 iteration and it did not converge. The code produces the correct convolution with the response function when used as a function in OriginC, but does not seem to work in the NLSF wizard.
for ( int i=0; i<Size; i++ )
{
for( int j=i; j<Size; j++ )
{
Temp = 0;
Temp = vIRF[i] * Amp * exp(-(vTime[j]-Shift)/Tau);
vConv[j] = vConv[j] + Temp;
}
}
Any assistance is greatly appreciated. TIA |
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larry_lan
China
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phenning
USA
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Posted - 09/22/2009 : 02:46:48 AM
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| I finally think I figured out the source of the problem. The number of datapoint returned was set to 100 in the NLSF dialog window - Settings tab - Fitted Curves item - X Data Type item - Unifrom Linear menu item. I changed the first menu box to "Same as Input Data" and all of the issues were resolved. Thank you for your help. |
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Convolution with NLSF Problem