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package PDL::Algorithm::Center;

# ABSTRACT: Various methods of finding the center of a sample

use strict;
use warnings;

require v5.10;

use feature 'state';

our $VERSION = '0.15';

use Carp;

use Try::Tiny;
use Safe::Isa;
use Ref::Util qw< is_arrayref is_ref is_coderef is_hashref >;

use Hash::Wrap ( { -as => '_wrap_hash' } );

use PDL::Algorithm::Center::Failure ':all';

use PDL::Algorithm::Center::Types -all;
use Types::Standard qw[ Optional ArrayRef Undef CodeRef Num ];
use Types::Common::Numeric -types;
use Type::Params qw[ compile_named ];

use PDL::Lite ();

use Exporter 'import';

our @EXPORT_OK = qw[ sigma_clip iterate ];

# as of Types::Standard 1.003_003, Bool coerces any value into a boolean,
# which we don't want.
use constant Bool => Types::Standard::Bool->no_coercions();

sub _weighted_mean_center {
    my ( $coords, $mask, $weight, $total_weight ) = @_;

    my $wmask = $mask * $weight;

    $total_weight //= $wmask->dsum;

    iteration_empty_failure->throw( 'weighted mean center: all elements excluded or sum(weight) == 0' )
      if $total_weight == 0;

    return ( $coords * $wmask->dummy( 0 ) )->xchg( 0, 1 )->dsumover / $total_weight;
}

sub _distance {

    my ( $prev, $current ) = @_;

    return sqrt( ( ( $prev->center - $current->center )**2 )->dsum );
}

sub _sigma_clip_initialize {    ## no critic (Subroutines::ProhibitManyArgs)

    my ( $init_clip, undef, $coords, $mask, $weight, $current, $work ) = @_;

    # initialize the sigma_clip specific fields the docs promise will be there
    $current->{dist} = undef;
    $current->{clip} = $init_clip;

    my $r2 = $work->{r2} = PDL->null;
    $r2 .= ( ( $coords - $current->center )**2 )->dsumover;

    $mask *= ( $r2 <= $init_clip**2 )
      if defined $init_clip;

    my $wmask = $work->{wmask} = $mask * $weight;

    $current->total_weight( $wmask->dsum );
    $current->nelem( $mask->sum );

    if ( $current->total_weight == 0 ) {