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<div class="title">Low-rank Matrix Factorization</div> </div>
<div class="ingroups"><a class="el" href="group__grp__unsuplearn.html">Unsupervised Learning</a></div></div>
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<dl class="user"><dt><b>About:</b></dt><dd></dd></dl>
<p>This module implements "factor model" for representing an incomplete matrix using a low-rank approximation [1]. Mathematically, this model seeks to find matrices U and V (also referred as factors) that, for any given incomplete matrix A, minimizes: </p>
<p class="formulaDsp">
\[ \|\boldsymbol A - \boldsymbol UV^{T} \|_2 \]
</p>
<p> subject to \(rank(\boldsymbol UV^{T}) \leq r\), where \(\|\cdot\|_2\) denotes the Frobenius norm. Let \(A\) be a \(m \times n\) matrix, then \(U\) will be \(m \times r\) and \(V\) will be \(n \times r\), in dimension, and \(1 \leq r \ll \min(m, n)\). This model is not intended to do the full decomposition, or to be used as part of inverse procedure. This model has been widely used in recommendation systems (e.g., Netflix [2]) and feature selection (e.g., image processing [3]).</p>
<dl class="user"><dt><b>Input:</b></dt><dd></dd></dl>
<p>The <b>input matrix</b> is expected to be of the following form: </p>
<pre>{TABLE|VIEW} <em>input_table</em> (
<em>row</em> INTEGER,
<em>col</em> INTEGER,
<em>value</em> DOUBLE PRECISION
)</pre><p>Input is contained in a table that describes an incomplete matrix, by having available entries specified as (row, column, value). The input matrix is expected to be based 1, which means row &gt;= 1, and col &gt;= 1. NULL values are not expected.</p>
<dl class="user"><dt><b>Usage:</b></dt><dd></dd></dl>
<p>Please find descriptions of SQL functions in <a class="el" href="lmf_8sql__in.html" title="SQL functions for low-rank matrix factorization.">lmf.sql_in</a></p>
<p>Output factors matrix U and V are in flatten format. </p>
<pre>RESULT AS (
matrix_u DOUBLE PRECISION[],
matrix_v DOUBLE PRECISION[],
rmse DOUBLE PRECISION
);</pre><p>Features correspond to row i is <code>matrix_u[i:i][1:r]</code>. Features correspond to column j is <code>matrix_v[j:j][1:r]</code>.</p>
<dl class="user"><dt><b>Examples:</b></dt><dd></dd></dl>
<ol type="1">
<li>Prepare an input table/view: <div class="fragment"><pre class="fragment">CREATE TABLE lmf_data (
column INT,
row INT,
value FLOAT8
);
</pre></div></li>
<li>Populate the input table with some data. e.g.: <div class="fragment"><pre class="fragment">INSERT INTO lmf_data VALUES (1, 1, 5.0);
INSERT INTO lmf_data VALUES (3, 100, 1.0);
INSERT INTO lmf_data VALUES (999, 10000, 2.0);
</pre></div></li>
<li>Call <a class="el" href="lmf_8sql__in.html#ac1acb1f0e1f7008118f21c83546a4602" title="Low-rank matrix factorization of a incomplete matrix into two factors.">lmf_igd_run()</a> stored procedure, e.g.: <div class="fragment"><pre class="fragment">SELECT madlib.lmf_igd_run(
<span class="stringliteral">&#39;lmf_model&#39;</span>, -- result table
<span class="stringliteral">&#39;lmf_data&#39;</span>, -- input table
<span class="stringliteral">&#39;row&#39;</span>, <span class="stringliteral">&#39;col&#39;</span>, <span class="stringliteral">&#39;value&#39;</span>, -- table column names
999, -- row dimension
10000, -- column dimension
3, -- rank (number of features)
0.1, -- stepsize
2, -- initial value scale factor
10, -- maximal number of iterations
1e-9); -- error tolerance
</pre></div> Example output (the exact result may not be the same): <div class="fragment"><pre class="fragment">NOTICE:
Finished low-rank matrix factorization <span class="keyword">using</span> incremental gradient
DETAIL:
table : lmf_data (row, col, value)
Results:
RMSE = 4.31144557397543e-05
Output:
view : SELECT * FROM lmf_model WHERE <span class="keywordtype">id</span> = 1
<a class="code" href="lmf_8sql__in.html#ac1acb1f0e1f7008118f21c83546a4602" title="Low-rank matrix factorization of a incomplete matrix into two factors.">lmf_igd_run</a>
-------------
1
(1 row)
</pre></div></li>
<li>Sanity check of the result. You may need a model id returned and also indicated by the function <a class="el" href="lmf_8sql__in.html#ac1acb1f0e1f7008118f21c83546a4602" title="Low-rank matrix factorization of a incomplete matrix into two factors.">lmf_igd_run()</a>, assuming 1 here, e.g.: <div class="fragment"><pre class="fragment">SELECT array_dims(matrix_u), array_dims(matrix_v) FROM lmf_model WHERE <span class="keywordtype">id</span> = 1;
</pre></div> Example output: <div class="fragment"><pre class="fragment"> array_dims | array_dims
--------------+----------------
[1:999][1:3] | [1:10000][1:3]
(1 row)
</pre></div></li>
<li>Query the result value, e.g.: <div class="fragment"><pre class="fragment">SELECT matrix_u[2:2][1:3] AS row_2_features FROM lmf_model WHERE <span class="keywordtype">id</span> = 1;
</pre></div> Example output (the exact result may not be the same): <div class="fragment"><pre class="fragment"> row_2_features
----------------------------------------------------------
{{0.51117920037359,0.169582297094166,0.837417622096837}}
(1 row)
</pre></div></li>
</ol>
<dl class="user"><dt><b>Literature:</b></dt><dd></dd></dl>
<p>[1] N. Srebro and T. Jaakkola. “Weighted Low-Rank Approximations.” In: ICML. Ed. by T. Fawcett and N. Mishra. AAAI Press, 2003, pp. 720–727. isbn: 1-57735-189-4.</p>
<p>[2] Simon Funk, Netflix Update: Try This at Home, December 11 2006, <a href="http://sifter.org/~simon/journal/20061211.html">http://sifter.org/~simon/journal/20061211.html</a></p>
<p>[3] J. Wright, A. Ganesh, S. Rao, Y. Peng, and Y. Ma. “Robust Principal Component Analysis: Exact Recovery of Corrupted Low-Rank Matrices via Convex Optimization.” In: NIPS. Ed. by Y. Bengio, D. Schuurmans, J. D. Lafferty, C. K. I. Williams, and A. Culotta. Curran Associates, Inc., 2009, pp. 2080–2088. isbn: 9781615679119. </p>
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