in reply to Viterbi application

G'day azheid,

"I have just enough coding experience to hang myself with a short rope. ... I tried to create a second similar matrix that stored the minimum distance to each node, but I am having trouble with correctly referencing the distance matrix."

I think you need some basic foundation knowledge.

In both of these lines, you're assigning an arrayref to an array: 

my @distance_mat=[];
...
my @vit_dist=[ [ 0] ];

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And in this line: 

${$vit_dist[$i]}[$j]=min(${$vit_dist[$i-1]}[$j]+${$distance_mat[$i]}[$
+j];

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you appear to be calling a min() function. You've failed to include a closing parenthesis so that leaves me guessing what is intended (and, potentially, what else has been left out or accidentally included). Perl has no min() function, Algorithm::Viterbi's documentation shows no min() function and you show no code for a min() function: I'm out of guesses.

Attempting to access a multi-dimensional array element with code like: 

${${$distance_mat[$i]}[$j]}[$k]

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is difficult to read and maintain: and, therefore, error-prone.

I suggest starting with "Perl references short introduction" and "Perl data structures intro".

Here's how I might have written the first piece of code you posted. I've reduced the number of elements from 10 to 2 for demonstration purposes. This should give you an idea of how you can (much simply) drill down into this sort of data structure and access individual elements. 

#!/usr/bin/env perl

use strict;
use warnings;

my $max_index = 1;
my $matrix;

for my $i (0 .. $max_index) {
    for my $j (0 .. $max_index) {
        for my $k (0 .. $max_index) {
            $matrix->[$i][$j][$k] = rand 1;
        }
    }
}

use Data::Dump;
dd $matrix;

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Output:

[
  [
    [0.290579816865833, 0.491432556740136],
    [0.888187692306143, 0.761365009561764],
  ],
  [
    [0.865674078359991, 0.284696276285089],
    [0.0562126863718184, 0.781856824452085],
  ],
]

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-- Ken

Replies are listed 'Best First'.
Re^2: Viterbi application
by azheid (Sexton) on Apr 06, 2014 at 21:52 UTC

    You are right, your implementation of the data matrix is much cleaner. I was not aware of that notation. min() is a subroutine that I did not include. It does exactly what it sounds like, returns the minimum of two values in a list.

    I will try to implement the code with this notation and see if the algorithm is easier to implement.

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      "min() is a subroutine that I did not include. It does exactly what it sounds like, returns the minimum of two values in a list."

      I did consider that might have been something like that (e.g. similar to List::Util's min() function); however, you're only providing a single value after min( in the code you posted.

      Here's an example of how ${$vit_dist[$i-1]}[$j]+${$distance_mat[$i]}[$j] might be evaluated: 

      $ perl -Mstrict -Mwarnings -le '
    my (@vit_dist, @distance_mat);
    $vit_dist[0][0] = 30;
    $distance_mat[1][0] = 12;
    my ($i, $j) = (1, 0);

    print ${$vit_dist[$i-1]}[$j]+${$distance_mat[$i]}[$j];
'
42

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      Perhaps you need a comma instead of a plus: 

      min(${$vit_dist[$i-1]}[$j], ${$distance_mat[$i]}[$j])

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      A liberalsplinklingofwhitespace may improve the readability of your code and reduce errors. :-)

      -- Ken

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[d/l]
[select]

        I stopped when I realized, for what seemed like the 10th consecutive try, that this code was not going to do what I wanted either

        I updated the original post with where I was intending to go with the min() line, however the code is not really doing the right thing

        My main problem is I cannot seem to translate the toy examples of viterbi into a piece of code that works regardless of the number of nodes in each row.

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      Implement seems to be my favorite word today

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