## April 20, 2009

### Compute the transpose of matrix using Hama

The transpose of a matrix is another matrix in which the rows and columns have been reversed. It will be used for SVD (Singular Value Decomposition).
+             +    +             +| a11 a12 a13 |    | a11 a21 a31 || a21 a22 a23 | => | a12 a22 a32 || a31 a32 a33 |    | a13 a23 a33 |+             +    +             +- A map task receives a row n as a key, and vector of each row as its value - emit (Reversed index, the entry with the given index)- Reduce task sets the reversed values

The transpose of 5,000 * 5,000 dense matrix took 12 mins using Hadoop/Hama (10 nodes). Why need to store the result? If we store the result, the locality will be provided for next steps, such as multiplication.

## April 10, 2009

### The ASF is ten years

The Apache Software Foundation was 10 years old two weeks ago. At that time, I was university student in Korea, I never dreamed that I would someday play with apache. Recently I'm quite busy at work but I'll do my best for ASF.

- https://blogs.apache.org/foundation/entry/the_asf_is_ten_years

## April 1, 2009

### Spam Filtering using Personalized Ontologies

This paper introduce a user-customized filter based on user-preferences and emails as an personalized ontologies.

- http://imsc-dmim.usc.edu/publications/2009_SAC_SWA_final.pdf