baseline mode

[just begginer]

Hi, I use Fityk 0.9.03

I have some question about using baseline mode.

Especially when the baseline have a big inclination.
Is it correct to subtract background by baseline manually?
OR Is there any problem?

The data with big background, then I want to subtract the background
by baseline.
But if the baseline is plotted by manually, the peak from crystal will
move some?

[Abbey Garant]

Did you ever find an answer to this?  I don't get how to include the baseline in my fits either!

[C L]

I would always suggest to use a 'normal' function for the background/baseline, e.g. use a cubic function for the background at the same time you are fitting peaks with Lorentz(or Voigt) as they have long tails. If you have multiple peaks/bands overlapping, the background might appear bigger than it actually is, and a baseline spline might 'cut away' actual intensity..

It would be nice to have a possibility to substract the function used for the background after fitting. Maybe make the first function of each data set to be the function describing the background by default. It would also be useful to be able to just fit this background function, if using a set of fitted functions copied from the last data set (fit won't work, if background levels are too different).

For further reading, I can recommend Meier (2005) On art and science in curve-fitting vibrational spectra (http://www.sciencedirect.com/science/article/pii/S0924203105000494).

[C L]

Ok, I just found out now that with Y=y-%f(x) I can do the subtraction of the background (via the fitted function f(x) (cubic in my case)).

How to do it: always use the function you want to define your baseline/background as the first function in each dataset, add functions for other bands/peaks, and fit everything until yuur satisfied. Afterwards use @*:Y=y-F[0](x) to subtract the background defining function from the data. Voila.

(Y=y-%f(x) is the way to substract function %f from the data over the range of x; @* means for all datasets; F[0] tells fityk to use the first function in each dataset for the subtraction)