NAME
VERSION
SYNOPSIS
DESCRIPTION
CRITERIA
METHODS
CONFIGURATION
DEPENDENCIES
BUGS AND LIMITATIONS
AUTHOR
LICENCE AND COPYRIGHT

NAME

Demeter::ScatteringPath::Rank - Ranking paths in a Feff calculation

VERSION

This documentation refers to Demeter version 0.9.26.

SYNOPSIS

This module provides a framework for evaluating path ranking formulas and associating the results with ScatteringPath objects. These rankings can be used to evaluate the importance of a path in a Feff calculation and, hopefully, provide some guidance about which paths to include in a fit.

This module is adapted from similar work by Karine Provost of Institut de Chimie et des Materiaux Paris-Est.

DESCRIPTION

Feff has long had a strange little feature called the "curved wave importance factor" that purports to be an assessment of the importance of a path. Paths with large importance factors should, presumably, be included in a fit. Unfortunately, the formula Feff uses to compute this number is not very reliable when applied to real world fitting problems.

This module, then, provides a framework for applying alternative importance calculations. This gives the user more information about the list of paths from a Feff calculation and hopefully provides better guidance for creating fitting models.

CRITERIA

feff: This is Feff's curve wave amplitude ratio.
akc: This is the sum over the k-range of |k*chi(k)|.
aknc: This is the sum over the k-range of |k^n*chi(k)|.
sqkc: This is the square root of the sum over the k-range of (k*chi(k))^2.
sqknc: This is the square root of the sum over the k-range of (k^n*chi(k))^2.
mkc: This is the sum over the k-range of |k*mag(chi(k))|.
mknc: This is the sum over the k-range of |k^n*mag(chi(k))|.
mft: This is the maximum value of |chi(R)| within the R range with the Fourier transform performed using the current value of the plotting k-weight.
sft: This is the sum over the R-range of |chi(R)| with the Fourier transform performed using the current value of the plotting k-weight.

METHODS

rank

Run the selected path ranking calculations on a ScatteringPath object and store the results in the rankings attribute, which is a hash reference. The keys of the referenced hash are given above.

  $sp -> rank($how, $plot);

$how specifies the ranking criterion. The configuration default will be used if not specified. If $plot is true, the path will be plotted in R.

normalize

For amplitude-valued rankings, scale each path in a list such that the largest path in the input list has a value of 100.

  $sp -> normalize(@list_of_sp);

$sp will be included in the list, but care will be taken not to include it twice.

get_rank

Return a path's value for a given test.

  $x = $sp->get_rank('akc');

get_rank_list

Return a list of identifying names for all the tests.

  @all = $sp -> get_rank_list;
  foreach my $r (@all) {
    print $r, " = ", $sp->get_rank($r);
  };

CONFIGURATION

The pathfinder->rank parameter is used to determine which criterion is used in the path interpretation. Other parameters in the pathfinder configuration group set the default k- and R-ranges for the evaluations. Finally, pathfinder->rank_high and pathfinder->rank_low set the cutoff between high, mid, and low importance paths in the path interpretation.

DEPENDENCIES

Demeter's dependencies are in the Build.PL file.

BUGS AND LIMITATIONS

Please report problems to the Ifeffit Mailing List (http://cars9.uchicago.edu/mailman/listinfo/ifeffit/)

Patches are welcome.

AUTHOR

Bruce Ravel (http://bruceravel.github.io/home)

http://bruceravel.github.io/demeter/

LICENCE AND COPYRIGHT

This module is free software; you can redistribute it and/or modify it under the same terms as Perl itself. See perlgpl.

This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.