Ops(3pm)

NAME
PDL::CCS::Ops - Low-level binary operations for compressed storage sparse PDLs

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

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

FUNCTIONS

  ccs_binop_align_block_mia
  Signature: (
    indx ixa(Ndims,NnzA); indx ixb(Ndims,NnzB); indx    istate(State);
    indx [o]nzai(NnzC);   indx [o]nzbi(NnzC);   indx [o]ostate(State);
    )

Partially aligns a pair of lexicographically sorted index-vector lists $ixa() and $ixb(), e.g. for block-wise incremental computation of binary operations over sparse index-encoded PDLs, assuming missing indices correspond to annihilators.

On return, the vectors $nzai and $nzbi hold indices into "NnzA" and "NnzB" respectively, and are constructed such that:

 ($ixa(,$nzai->slice("0:$nzci_max")) == $ixb(,$nzbi->slice("0:$nzci_max"))

At most "NnzC" alignments are performed, and alignment ceases as soon as any of the PDLs $ixa(), $ixb(), $nzai(), or $nzbi() has been exhausted.

The parameters $istate() and $ostate() hold the state of the algorithm, for incremental block-wise computation at the perl level. Each state PDL is a 7-element PDL containing the following values:

 INDEX LABEL       DESCRIPTION
 -----------------------------------------------------------------------
   0   nnzai       minimum offset in NnzA of current $ixa() value
   1   nnzai_nxt   minimum offset in NnzA of next $ixa() value
   2   nnzbi       minimum offset in NnzB of current $ixb() value
   3   nnzbi_nxt   minimum offset in NnzB of next $ixb() value
   4   nnzci       minimum offset in NnzC of current ($ixa(),$ixb()) value pair
   5   nnzci_nxt   minimum offset in NnzC of next ($ixa(),$ixb()) value pair
   6   cmpval      3-way comparison value for current ($ixa(),$ixb()) value pair

For computation of the first block, $istate() can be safely set to "zeroes(long,7)".

Repetitions may occur in input index PDLs $ixa() and $ixb(). If an index-match occurs on such a "run", all pairs of matching values are added to the output PDLs.

All alignments have been performed if:

 $ostate(0)==$NnzA && $ostate(1)==$NnzB

WARNING: this alignment method ignores index-vectors which are not present in both $ixa() and $ixb(), which is a Good Thing if your are feeding the aligned values into an operation for which missing values are annihilators:

 $missinga * $bval     == ($missinga * $missingb)  for each $bval \in $b, and
 $aval     * $missingb == ($missinga * $missingb)  for each $aval \in $a

This ought to be the case for all operations if missing values are "BAD" (see PDL::Bad), but might cause unexpected results if e.g. missing values are zero and the operation in question is addition.

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

ACKNOWLEDGEMENTS
Perl by Larry Wall.

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

KNOWN BUGS
No support for (pseudo)-threading.

AUTHOR
Bryan Jurish <moocow@cpan.org>

  Copyright Policy
All other parts Copyright (C) 2007-2024, 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)