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Subject:

Rate Analysis/Fitting problem: setting start values or custom function

From:

Christoph Hartlmüller <[log in to unmask]>

Reply-To:

CcpNmr software mailing list <[log in to unmask]>

Date:

Fri, 10 May 2013 19:28:36 +0200

Content-Type:

text/plain

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 text/plain (38 lines)
 ```Hi CCPN users, I have some trouble using the Rate Analysis function in Analysis (Version 2.2. Release 1). I managed to setup an NMR series, fit a function and look at the plots of the fits. The problem concerns the fitting: I have a series of HSQC spectra that were recorded using different delay times. In this case, we observe signals that increase with increasing delay times. So the data that we want to fit is of the type (I selected this type in Analysis) A*exp(-Bx) + C where B and C are positive, A is negative and the absolute value of C is roughly equal to that of A Now the problem is, that in the fit results Analysis only gets positive values for A and negative values for B and C. So the fitting curve is completely wrong. So the questions are basically: Is there a possibility to set starting values for the parameters A,B and C or limited them to a certain range? If no, is it possible to setup a custom equation, like -A*exp(-Bx) + C ? To narrow down the problem: If I choose some other equation (for example linear) I can see that Analysis roughly gets the data fitted (as much as possible of course). So the setup is ok, it's just that the fitting procedure is not getting anywhere near the correct solution. Also, I phase-shifted the spectra 180 degree to make everything negative, since A and C should then switch sign. However the fitting does not work any longer since the result list is complete empty. My guess is that Analysis does not pick the peaks in the other HSQCs anymore as they are now negative ( I did switch "Peak=> Peak Finding => Extrema to search for" to "positive and negative" ; that's how I created the peak list at the first place ) Thank you and best regards, Christoph Hartlmueller ```

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