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Computing for Science

The Computing for Science (CS) group supports ILL scientists, students and visitors in a number of activities including data analysis, instrument simulation and sample simulation.

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Clickfit - Interactive data fitting

for Fitfun version 7.0 onwards, R. Ghosh, ILL, August 2006

Summary

This graphical controlling program allows a diverse set of programs for fitting data to be constructed easily. The fitting engine uses the fitfun library which incorporates Powell's resilient minimisation routine VA05A, calculating numerical derivatives. This can be applied to a large range of problems. Apart from controlling fits two aspects of major interest in the present version are:

  • the ability to treat sequences of data
  • the ability to fit multiple data sets simultaneously fitfun_m

    These are the principal features required in modern data treatment where an environment parameter (temperature etc.) is scanned, and the set of data can be treated together. The second case is highly relevant for neutron scattering data where selective deuteration can be used to emphasise features of otherwise similar samples.

    A technical description is available to help programmers maintain the fitting suite. A simplified example shows a small application, and illustrates use of COMMON variables used by fitfun.

The User's View of Clickfit

There are two versions of the program, Clickfit for treating one or sequences of individual datasets. Clickfit_m is adapted to treat the case of controlling simultaneous fitting of several datasets, where more selective control of fitting parameters is required.

Often fitting programs are written with several similar variants, or certain control parameters can be predefined for specific tasks. On launching Clickfit the first frame contains the editable list of program variants available. The most recently used program is highlighted.

The programs use a number of common components; to simplify relocating onto other computers the fields here contain the important placement of the graphics package PGPLOT and the current default program directory. The latter would normally contain the executable programs and their clickfit configuration files and variants, and thus make it simple to re-install the set on another computer with a different directory structure. Once selected these options may be edited. Clicking on ACCEPT starts the selected program, passing to an optional PRELUDE page.

The Prelude

To allow programmers a wide choice of additional options before entering the principal part of the fitting program there is a configurable prelude section where values can be entered for later use. Here a number of options for wetlay are shown:

After any edition pass to the next step with the ACCEPT button.

Functions offered by Clickfit

Essentially the same GUI interface routines can control either single data fits (using library fitfun v7.0) or simultaneous fitting of several sets (fitfun_m v7.1) This section offers most of the original features of the fitfun command line.

Menu options

File
    Save parameters        into a *.ffn or *.ffm file, used on restart.
    Append to list file    outputs current fit information to listfile
    Read in                brings up data input panel
    Exit                   terminates program
Parameters
    edit parameter         edit parameter and step
    Link steps             parameters grouped to be varied with the same step 
    Copy parameter set*    copies parameters from one dataset for another
Fitting
    Limit x Ranges         Restrict fitting to three x ranges (max)        
    Step size              The fractional step multiplied by the parameter
                            step size for numerical derivatives
Graphics
    Set scales             sets scale limits for x and y
    Append PostScript plot add a plot of the current fit to file
    Cursor                 toggle cursor on/off in next display
    Title                  Add title to next plots
    Write plot datafile    Write out fits and data as ascii file
View
    View log               Displays current log file
    View sets*              lists current sets
Extras
    Special Function        (J command - often a display/output
                                   option
    Command                Access to basic fitfun command line
    Debug                  Toggles on and off - shows comms
Memo                       up to 4 manual commands can be stored/recalled
Help                       Help file (or other file if configured)

Modify parameters          Double click on parameter line
Buttons
  Clear data*              resets all sets
  Show all parameters*     displays parameters for all sets
  Select set for display*  give set number for current display
  Fit Sequence+            fit a sequence of data using input control file
  Make Sequence+           will filter a sequence of filenames to treat
  SAVE                     SAVE current parameter (reread at next start)
  Restart                  when configured - restart prgram
  Display Data             display current data (with/without cursor) 
  Trial Fit                Show current model calculation
  Fit Iterations           iterate the indicated (max) number of times
  EXIT                     EXIT program (please AVOID terminating window)

+ Clickfit
* Clickfit_m


Data treatment proceeds through the stages of READ/Trial/Iterate../(SAVE)/EXIT

Sequences

Before a sequence can be treated an initial dataset must be fitted to set the initial parameters to approximate values for the sequence. The information for each member of the sequence is read from a control file; a simple example follows: 

Fileseq.fsq...
gtst sequence    title 
fitseq.out       output filename
T                Reuse first trial (T) or update (U)parameters for next set 
50               Number of iterations
r.spc  3.5       input data for each fit
s.spc  4.2                    :
t.spc  4.9                    :

When (typically) only a filename is used for each set of data to be treated the Make sequence button will bring up a window to create a control file automatically, which is then used to treat the (filtered) filenames therein:

The filter allows an initial set of files to be chosen; this leads to the next window to allow a selection and order to be completed with the panel allowing single/multiple selects etc., and the fits performed.

Installation and Use

The program scripts may be found at: 
ftp://ftp.ill.fr/pub/cs/clickfit
Clickfit requires the wish/tcl/tk package and graphics, using pgplot, also must be installed. When clickfit runs for the first time it will need to informed of the default directories for programs and work

PC and Windows

The program is started as a batch file (.bat) It is assumed that the program is run using the prop package and this contains all the prerequisites. The two files clickfit.bat and clickfit_m.bat are simply copied to the project program directory and (if necessary) added to the program selector.

Unix/Linux/OSX

The plotting environment variable PGPLOT_DIR should be set to find the PGPLOT xserver program and fonts. The clickfit.tcl and clickfit_m.tcl files may require editing on the first line to use the local version of wish, alternatively they may be started with the command 

 % wish clickfit.tcl 
Applications

Reflectometry   flyg, wetlay, drydoc ...etc 
SANS            polymer, sasfit4, ... 
Backscattering  firr
Diffraction     f24s, flg, ...

Acknowledgements

The routines have been tested with the suite of programs for neutron reflectivity data analysis programs and the encouragement of the author, Professor A. Rennie who has made them available for use at the ILL, is gratefully acknowledged here.