lake: Lake Desmearing for Small-Angle Scattering

Copyright (c) 1991-2010, Pete R. Jemian

COMPILE

for UNIX or Linux or Cygwin

make clean # remove any built object files make # compile "lake" executable make test # run a test case as an example make diff # compare the test case with known example more xxx.log # view the test case

CITATION

Use this reference to cite this code in a publication.

PhD Thesis, 1990, Northwestern University, Evanston, IL, USA, Pete R. Jemian. http://jemian.org/pjthesis.pdf

USE

These instructions are very limited. Additional help might be available in the Theory chapter of my PhD thesis: http://jemian.org/pjthesis.pdf

Compile the program as above and run the "lake" executable. Hint: This command should do it all: make clean diff Output from "make diff" should be a difference in when the executable was built. Such as::

/bin/rm -f *.o core *%
gcc    -c -o lake.o lake.c
gcc    -c -o hunt.o hunt.c
gcc    -c -o stats.o stats.c
gcc    -c -o toolbox.o toolbox.c
gcc    -c -o recipes.o recipes.c
gcc -o lake lake.o hunt.o stats.o toolbox.o recipes.o -lm
./lake < xxx.inp > xxx.log
diff test_xxx.log xxx.log
3c3
<  This executable was built Nov  9 2010, 09:55:20
---
>  This executable was built Nov  9 2010, 10:01:44
make: *** [diff] Error 1

No "install" methods are provided. The Makefile will build "lake" executable as a shared-object. (Not static).

Input data will be provided in an ASCII TEXT file as three columns (Q I dI) separated by white space. Units must be compatible. (I and dI must have same units)

:Q: scattering vector :I: measured SAS intensity :dI: estimated uncertainties of I (usually standard deviation)

Note that dI MUST be provided and MUST not be zero.

NOTES

*revised to compile on:

• Linux gcc

• Solaris Sun Workshop C

• Windows 95/98/NT Metrowerks CodeWarrior

• Macintosh Metrowerks CodeWarrior

• Macintosh Symantec C

• 1994-02-04

  • direct translation of LAKE.FOR
  • which would not run correctly under System 7
  • (Some compiler error that would not pass array DC(*) into subroutine SMEAR.)

• 2002-Sept-18:

  • users of Windows version report errors associated with file names

• Probably a bug was edited in.

HISTORY:

• lake.c was derived from the FORTRAN program: Lake.FOR 25 May 1991
• Lake.FOR was created by Pete Jemian, (http://jemian.org/pjthesis.pdf)
• ref: J.A. Lake; ACTA CRYST 23 (1967) 191-194.
• by: Pete R. Jemian, Late-Nite(tm) Software

BIBLIOGRAPHY

• O. Glatter; ACTA CRYST 7 (1974) 147-153
• W.E. Blass & G.W.Halsey (1981). "Deconvolution of Absorption Spectra." New York City: Academic Press
• P.A. Jansson. (1984) "Deconvolution with Applications in Spectroscopy." New York City: Academic Press.
• G.W.Halsey & W.E. Blass. "Deconvolution Examples" in "Deconvolution with Applications in Spectroscopy." Ed. P.A. Jansson. (see above)

PURPOSE

This program applies the iterative desmearing technique of Lake to small-angle scattering data. The way that the program works is that the user selects a file of data (x,y,dy) to be desmeared. If a file was not chosen, the program will end. Otherwise the user is then asked to specify the slit-length (in the units of the x-axis); the X at which to begin fitting the last data points to a power-law of X, the output file name, and the number of iterations to be run. Then the data file is opened, the data is read, and the data file is closed. The program begins iterating and shows an indicator of progress on the screen in text format.

It is a mistake to run this program on data that has been desmeared at least once (by this program) as you will see. The problem is that the program expects that the input data has been smeared, NOT partially desmeared. Lake's technique should be made to iterate with the original, smeared data and subsequent trial solutions of desmeared data.

The integration technique used by this program to smear the data is the trapezoid-rule where the step-size is chosen by the spacing of the data points themselves. A linear interpolation of the data is performed. To avoid truncation effects, a power-law extrapolation of the intensity is made for all values beyond the range of available data. This region is also integrated by the trapezoid rule. The integration covers the region from l = 0 up to l = lo. (see routine SMEAR). This technique allows the slit-length weighting function to be changed without regard to the limits of integration coded into this program.