Ted Pedersen > Math-SparseVector > Math::SparseVector

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Module Version: 0.04   Source  

NAME ^

Math::SparseVector - Supports sparse vector operations such as setting a value in a vector, reading a value at a given index, obtaining all indices, addition and dot product of two sparse vectors, and vector normalization.

MODULE HISTORY ^

This module is the successor to Sparse::Vector, which was re-cast into this new namespace in order to introduce another module Math::SparseMatrix, which makes use of this module.

SYNOPSIS ^

  use Math::SparseVector;

  # creating an empty sparse vector object
  $spvec=Math::SparseVector->new;

  # sets the value at index 12 to 5
  $spvec->set(12,5);

  # returns value at index 12
  $value = $spvec->get(12);

  # returns the indices of non-zero values in sorted order
  @indices = $spvec->keys;

  # returns 1 if the vector is empty and has no keys
  if($spvec->isnull) {
    print "vector is null.\n";
  }
  else  {
    print "vector is not null.\n";
  }

  # print sparse vector to stdout
  $spvec->print;

  # returns the string form of sparse vector
  # same as print except the string is returned
  # rather than displaying on stdout
  $spvec->stringify;

  # adds sparse vectors v1, v2 and stores 
  # result into v1
  $v1->add($v2);

  # adds binary equivalent of v2 to v1
  $v1->binadd($v2);
  # binary equivalnet treats all non-zero values 
  # as 1s

  # increments the value at index 12
  $spvec->incr(12);

  # divides each vector entry by a given divisor 4
  $spvec->div(4);

  # returns norm of the vector
  $spvec_norm = $spvec->norm;

  # normalizes a sparse vector
  $spvec->normalize;

  # returns dot product of the 2 vectors
  $dotprod = $v1->dot($v2);

  # deallocates all entries
  $spvec->free;

USAGE NOTES ^

1. Loading Math::SparseVector Module

To use this module, you must insert the following line in your Perl program before using any of the supported methods.

    use Math::SparseVector;
2. Creating a Math::SparseVector Object

The following line creates a new object of Math::SparseVector class referred with the name 'spvec'.

    $spvec=Math::SparseVector->new;

The newly created 'spvec' vector will be initially empty.

3. Using Methods

Now you can use any of the following methods on this 'spvec' Math::SparseVector object.

1. set(i,n) - Sets the value at index i to n
         # equivalent to $spvec{12}=5;
         $spvec->set(12,5); 
2. get(i) - Returns the value at index i
         # equivalent to $value=$spvec{12};
         $value = $spvec->get(12); 
3. keys() - Returns the indices of all non-zero values in the vector
         # equivalent to @keys=sort {$a <=> $b} keys %spvec;
         @indices = $spvec->keys;
4. isnull() - Returns 1 if the vector is empty and has no keys
         # similar to
         # if(scalar(keys %spvec)==0) {print "vector is null.\n";}
         if($spvec->isnull) { print "vector is null.\n"; }
5. print() - Prints the sparse vector to stdout - Output will show a list of space separated 'index value' pairs for each non-zero 'value' in the vector.
         # similar to
         # foreach $ind (sort {$a<=>$b} keys %spvec)
             # { print "$ind " . $spvec{$ind} . " "; }
         $spvec->print;
6. stringify() - Returns the vector in a string form. Same as print() method except the vector is written to a string that is returned instead of displaying onto stdout
         # the below will do exactly same as $spvec->print;
         $string=$spvec->stringify;
         print "$string\n";
7. v1->add(v2) - Adds contents of v2 to vector v1.
         Similar to v1+=v2

         $v1->add($v2);
         If v1 = (2,  , , 5, 8, ,  , , 1)
         &  v2 = ( , 1, , 3,  , , 5, , 9)
         where blanks show the 0 values that are not stored in 
         Math::SparseVector.

         After      $v1->add($v2); 
         v1 = (2, 1, , 8, 8, , 5, , 10) and v2 remains same
8. v1->binadd(v2) - Binary equivalent of v2 is added into v1. Binary equivalent of a vector is obtained by setting all non-zero values to 1s.
         If v1 = (1,  , , 1, 1, ,  , , 1)
         &  v2 = ( , 1, , 1,  , , 1, , 1)
         Then, after v1->binadd(v2),
         v1 will be (1, 1, , 1, 1, , 1, , 1).

         If v1 = (1,  , , 1, 1, ,  , , 1)
         &  v2 = ( , 1, , 3,  , , 5, , 9)
         v1->binadd(v2);
         will set v1 to (1, 1, , 1, 1, , 1, , 1).
9. incr(i) - Increments the value at index i
         # is similar to $spvec{12}++;
         $spvec->incr(12);
10. div(n) - Divides each vector entry by a given divisor n
         $spvec->div(4);
         If spvec = (2,  , , 5, 8, ,  , , 1)
         Then, $spvec->div(4)
         will set spvec to (0.5, , , 1.25, 2, , , , 0.25)
11. norm() - Returns the norm of a given vector
         $spvec_norm = $spvec->norm;
         If spvec = (2,  , , 5, 8, ,  , , 1)
         $spvec->norm will return the value 
         = sqrt(2^2 + 5^2 + 8^2 + 1)
         = sqrt(4 + 25 + 64 + 1)
         = 9.69536
12. v1->dot(v2) - Returns the dot product of two vectors
         $dotprod = $v1->dot($v2);
         If v1 = (2,  , , 5, 8, ,  , , 1)
                 &  v2 = ( , 1, , 3,  , , 5, , 9)
         v1->dot(v2) returns
         5*3 + 1*9 = 15 + 9 = 24
13. free() - Deallocates all entries and makes the vector empty
         $spvec->free;
         will set spvec to null vector ()

AUTHORS ^

Amruta Purandare, University of Pittsburgh amruta at cs.pitt.edu

Ted Pedersen, University of Minnesota, Duluth tpederse at d.umn.edu

Mahesh Joshi, Carnegie-Mellon University maheshj at cmu.edu

COPYRIGHT AND LICENSE ^

Copyright (c) 2006-2008, Amruta Purandare, Ted Pedersen, Mahesh Joshi

This program is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation; either version 2 of the License, or (at your option) any later version.

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. See the GNU General Public License for more details.

You should have received a copy of the GNU General Public License along with this program; if not, write to

 The Free Software Foundation, Inc.,
 59 Temple Place - Suite 330,
 Boston, MA  02111-1307, USA.
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