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Date: Mon, 13 Oct 2008 00:28:46 -0700 (PDT)
From: "Samuel Guo (JIRA)" <jira@apache.org>
To: hama-dev@incubator.apache.org
Subject: [jira] Commented: (HAMA-80) Add identity(int m, int n) which
 returns an m-by-n matrix with ones on the diagonal and zeros elsewhere.
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    [ https://issues.apache.org/jira/browse/HAMA-80?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12638959#action_12638959 ] 

Samuel Guo commented on HAMA-80:
--------------------------------

Why we need m & n both?
In linear algebra, the identity matrix or unit matrix of size n is the n-by-n square matrix with ones on the main diagonal and zeros elsewhere.
And I don't think it's good to store an identity matrix as DenseMatrix. It may not efficient.

Maybe we can create another class, sth like:

class IdentityMatrix implements Matrix {

....

public double get(int i, int j) throws IOException {
  return (i==j)?1:0;
}

....

}

it is not neccessary to store the matrix in hbase. 


> Add identity(int m, int n) which returns an m-by-n matrix with ones on the diagonal and zeros elsewhere.
> --------------------------------------------------------------------------------------------------------
>
>                 Key: HAMA-80
>                 URL: https://issues.apache.org/jira/browse/HAMA-80
>             Project: Hama
>          Issue Type: New Feature
>          Components: implementation
>            Reporter: Edward J. Yoon
>            Assignee: Edward J. Yoon
>            Priority: Minor
>             Fix For: 0.1.0
>
>         Attachments: HAMA-80.patch
>
>
> double[][] X;
>       for (int i = 0; i < m; i++) {
>          for (int j = 0; j < n; j++) {
>             X[i][j] = (i == j ? 1.0 : 0.0);
>          }
>       }

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