NAME

PDL::CCS::Utils - Low-level utilities for compressed storage sparse PDLs

SYNOPSIS

 use PDL;
 use PDL::CCS::Utils;

 ##---------------------------------------------------------------------
 ## ... stuff happens

FUNCTIONS

Non-missing Value Counts

nnz

  Signature: (a(N); int+ [o]nnz())

Get number of non-zero values in a PDL $a(); For 1d PDLs, should be equivalent to:

 $nnz = nelem(which($a!=0));

For k>1 dimensional PDLs, projects via number of nonzero elements to N-1 dimensions by computing the number of nonzero elements along the the 1st dimension.

nnz does not process bad values. It will set the bad-value flag of all output piddles if the flag is set for any of the input piddles.

nnza

  Signature: (a(N); eps(); int+ [o]nnz())

Like nnz() using tolerance constant $eps(). For 1d PDLs, should be equivalent to:

 $nnz = nelem(which(!$a->approx(0,$eps)));

nnza does not process bad values. It will set the bad-value flag of all output piddles if the flag is set for any of the input piddles.

Encoding Utilities

ccs_encode_pointers

  Signature: (indx ix(Nnz); indx N(); indx [o]ptr(Nplus1); indx [o]ixix(Nnz))

General CCS encoding utility.

Get a compressed storage "pointer" vector $ptr for a dimension of size $N with non-missing values at indices $ix. Also returns a vector $ixix() which may be used as an index for $ix() to align its elements with $ptr() along the compressed dimension.

The induced vector $ix->index($ixix) is guaranteed to be stably sorted along dimension $N():

 \forall $i,$j with 1 <= $i < $j <= $Nnz :

  $ix->index($ixix)->at($i) < $ix->index($ixix)->at($j)   ##-- primary sort on $ix()
 or
  $ixix->at($i)             < $ixix->at($j)               ##-- ... stable

ccs_encode_pointers does not process bad values. It will set the bad-value flag of all output piddles if the flag is set for any of the input piddles.

Decoding Utilities

ccs_decode_pointer

  Signature: (indx ptr(Nplus1); indx proj(Nproj); indx [o]projix(NnzProj); indx [o]nzix(NnzProj))

General CCS decoding utility.

Project indices $proj() from a compressed storage "pointer" vecotr $proj(). If unspecified, $proj() defaults to:

 sequence($ptr->dim(0))

ccs_decode_pointer does not process bad values. It will set the bad-value flag of all output piddles if the flag is set for any of the input piddles.

Indexing Utilities

ccs_xindex2d

  Signature: (which(Ndims,Nnz); a(Na); b(Nb); [o]ab(Nab); [o]nab())

Compute indices along dimension NNz of $which() corresponding to any combination of values in the Cartesian product of $a() and $b(). Appropriate for indexing a 2d sparse encoded PDL with non-missing entries at $which() via the ND-index piddle $a->slice("*1,")->cat($b)->clump(2)->xchg(0,1), i.e. all pairs $ai,$bi with $ai in $a() and $bi in $b(). $a() and $b() values must be be sorted in ascending order

In list context, returns a list ($ab,$nab), where $nab() is the number of indices found, and $ab are those Nnz indices. In scalar context, trims the output vector $ab() to $nab() elements.

ccs_xindex2d does not process bad values. It will set the bad-value flag of all output piddles if the flag is set for any of the input piddles.

Debugging Utilities

ccs_dump_which

  Signature: (indx which(Ndims,Nnz); SV *HANDLE; char *fmt; char *fsep; char *rsep)

Print a text dump of an index PDL to the filehandle HANDLE, which default to STDUT. $fmt is a printf() format to use for output, which defaults to "%d". $fsep and $rsep are field-and record separators, which default to a single space and $/, respectively.

ccs_dump_which does not process bad values. It will set the bad-value flag of all output piddles if the flag is set for any of the input piddles.

ACKNOWLEDGEMENTS

Perl by Larry Wall.

PDL by Karl Glazebrook, Tuomas J. Lukka, Christian Soeller, and others.

KNOWN BUGS

Probably many.

AUTHOR

Bryan Jurish <moocow@cpan.org>

Copyright Policy

Copyright (C) 2007-2013, Bryan Jurish. All rights reserved.

This package is free software, and entirely without warranty. You may redistribute it and/or modify it under the same terms as Perl itself.

SEE ALSO

perl(1), PDL(3perl)

cpanm PDL::CCS

perl -MCPAN -e shell
install PDL::CCS