Fitting three spectra simultaneously with the same parameters

[Simon Kohn]

Hello, I am new to fityk and I like a lot of things about it. I have mostly used the GUI but am exploring the use of the command line also. My operating system is Mac 10.12.6.

My problem is that I have three spectra (they are FTIR spectra of the same sample but with different polarisations). I need the position and width of each peak to be forced to be the same between the three spectra but allow the height to vary. It looks like I should be able to do this in the GUI using cmdR then clicking "all datasets" and unchecking "fit each dataset separately". It doesn't work though. I also tried typing fit@* in the command line, but again each spectrum is fitted with completely different parameters.

What am I doing wrong? Any help much appreciated.

Simon

[Marcin Wojdyr]

Hi Simon,

Usually, the position and width of each peak is an independent parameter.
To use the same parameter for the position of the first function in
each dataset type:

@*: F[0].center = @0.F[0].center

And similarly, to set the width of each first function to the width of
the first function from the first dataset do:

@*: F[0].hwhm = @0.F[0].hwhm

Best wishes,
Marcin

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[Simon Kohn]

Hi Marcin,

Thanks for the quick reply. As I said I am very new to Fityk so still trying to understand the approach. If I have 12 peaks (for example) do I have to write this separately for each function, so F[0]......F[11]? Also more fundamentally do I have to write a script with all these instructions, or if I type the rule into the command line will it remember the constraint each time I do a new fit of the datasets? Unfortunately I have been doing something wrong as typing your text into the command line has not had the desired effect.

Sorry about the very basic questions. I will keep trying.

Thanks,

Simon

On Thursday, August 1, 2019 at 12:01:32 AM UTC+1, Marcin Wojdyr wrote:

Hi Simon,

Usually, the position and width of each peak is an independent parameter.
To use the same parameter for the position of the first function in
each dataset type:

@*: F[0].center = @0.F[0].center

And similarly, to set the width of each first function to the width of
the first function from the first dataset do:

@*: F[0].hwhm = @0.F[0].hwhm

Best wishes,
Marcin


On Wed, 31 Jul 2019 at 15:10, Simon Kohn <gl...@bristol.ac.uk> wrote:
>
> Hello, I am new to fityk and I like a lot of things about it. I have mostly used the GUI but am exploring the use of the command line also. My operating system is Mac 10.12.6.
>
> My problem is that I have three spectra (they are FTIR spectra of the same sample but with different polarisations). I need the position and width of each peak to be forced to be the same between the three spectra but allow the height to vary. It looks like I should be able to do this in the GUI using cmdR then clicking "all datasets" and unchecking "fit each dataset separately". It doesn't work though. I also tried typing fit@* in the command line, but again each spectrum is fitted with completely different parameters.
>
> What am I doing wrong? Any help much appreciated.
>
> Simon
>
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[Marcin Wojdyr]

Hi Simon,

yes, you'd need to do it separately for each function.
The commands should work regardless if they are in a script file or
typed directly in the program.
Have you made it work? For example, if you type:
@1.F[0].center = @0.F[0].center
the first functions (first in the order in which they were added) in
the first two datasets should have the same position.

Marcin

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[Simon Kohn]

Hi Marcin,

Yes, I am getting somewhere now! My data are quite complicated, so it will take some time to perfect the fits, but I understand the principle now and it is definitely working. I think I was confused by the fact that the functions are listed as _1, _2, _3 etc in the table in the top right pane of the gui, but (in the example of two spectra being processed together), _1 and _2 are F[0], _3 and _4 are F[1], _5 and _6 are F[2] etc.

Many thanks for providing the software to the community and for your personalised help.

Simon

> To view this discussion on the web visit https://groups.google.com/d/msgid/fityk-users/CACaHzQX6OfVp3KnjBnnwxocn%3D%2Bmdw3Hxug_U%3DWJP%2BqV8%3Den38A%40mail.gmail.com.