psteitz 2004/01/14 23:29:39
Modified: math/xdocs/userguide random.xml
Log:
Added data generation doc.
Revision Changes Path
1.6 +48 -4 jakarta-commons/math/xdocs/userguide/random.xml
Index: random.xml
===================================================================
RCS file: /home/cvs/jakarta-commons/math/xdocs/userguide/random.xml,v
retrieving revision 1.5
retrieving revision 1.6
diff -u -r1.5 -r1.6
--- random.xml 11 Jan 2004 19:35:22 -0000 1.5
+++ random.xml 15 Jan 2004 07:29:38 -0000 1.6
@@ -127,7 +127,7 @@
<code>nextSecureHexString</code> generates hex characters in 40-byte "chunks"
using a 3-step process:
<ol>
- <li>20 random bytes are generated using the underlying
<code>SecureRandom</code>.</li>
+ <li>20 random bytes are generated using the underlying
<code>SecureRandom.</code></li>
<li>SHA-1 hash is applied to yield a 20-byte binary digest.</li>
<li>Each byte of the binary digest is converted to 2 hex digits</li></ol>
Similarly to the secure random number generation methods,
<code>nextSecureHexString</code>
@@ -164,8 +164,52 @@
<subsection name='2.5 Generating data "like" an input file' href="empirical">
<p>
- This is yet to be written. Any contributions will be gratefully accepted!
- </p>
+ Using the <code>ValueServer</code> class, you can generate data based on the
+ values in an input file in one of two ways:
+ <dl>
+ <dt>Replay Mode</dt>
+ <dd> The following code will read data from <code>url</code>
+ (a <code>java.net.URL</code> instance), cycling through the values in the
+ file in sequence, reopening and starting at the beginning again when all
+ values have been read.
+ <source>
+ ValueServer vs = new ValueServer();
+ vs.setValuesFileURL(url);
+ vs.setMode(ValueServer.REPLAY_MODE);
+ vs.resetReplayFile();
+ double value = vs.getNext();
+ // ...Generate and use more values...
+ vs.closeReplayFile();
+ </source>
+ The values in the file are not stored in memory, so it does not matter
+ how large the file is, but you do need to explicitly close the file as above.
+ The expected file format is \n -delimited (i.e. one per line) strings
+ representing valid floating point numbers.
+ </dd>
+ <dt>Digest Mode</dt>
+ <dd>When used in Digest Mode, the ValueServer reads the entire input file
+ and estimates a probability density function based on data from the file.
+ The estimation method is essentially the <a
href="http://nedwww.ipac.caltech.edu/level5/March02/Silverman/Silver2_6.html";>
+ Variable Kernel Method</a> with Gaussian smoothing. Once the density has been
+ estimated, <code>getNext()</code> returns random values whose probability
+ distribution matches the empirical distribution -- i.e., if you generate a
large
+ number of such values, their distribution should "look like" the distribution
of
+ the values in the input file. The values are not stored in memory in this
case either,
+ so there is no limit to the size of the input file. Here is an example:
+ <source>
+ ValueServer vs = new ValueServer();
+ vs.setValuesFileURL(url);
+ vs.setMode(ValueServer.DIGEST_MODE);
+ vs.computeDistribution(500); //Read file and estimate distribution using 500
bins
+ double value = vs.getNext();
+ // ...Generate and use more values...
+ </source>
+ See the javadoc for <code>ValueServer</code> and
<code>EmpiricalDistribution</code>
+ for more details. Note that <code>computeDistribution()</code> opens and
closes
+ the input file by itself.
+ </dd>
+ </dl>
+ </p>
</subsection>
</section>
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