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Tools.pm  view on Meta::CPAN

However, there is two methods of interpolation:

Example, we have only three numbers: 5, 6 and 7.

Method 1: The most common is to say that 5 and 7 lays on the 25- and
75-percentile. This method is used in Acme::Tools.

Method 2: In Oracle databases the least and greatest numbers
always lay on the 0- and 100-percentile.

As an argument on why Oracles (and others?) definition is not the best way is to
look at your data as for instance temperature measurements.  If you
place the highest temperature on the 100-percentile you are sort of
saying that there can never be a higher temperatures in future measurements.

A quick non-exhaustive Google survey suggests that method 1 here is most used.

The larger the data sets, the less difference there is between the two methods.

B<Extrapolation:>

Tools.pm  view on Meta::CPAN

=head2 bfdimensions

Input, two numeric arguments: Capacity and error_rate.

Outputs an array of two numbers: m and k.

  m = - n * log(p) / log(2)**2   # n = capacity, m = bits in filter (divide by 8 to get bytes)
  k = log(1/p) / log(2)          # p = error_rate, uses perls internal log() with base e (2.718)

...that is: m = the best number of bits in the filter and k = the best
number of hash functions optimized for the given capacity (n) and
error_rate (p). Note that k is a dependent only of the error_rate.  At
about two percent error rate the bloom filter needs just the same
number of bytes as the number of keys.

 Storage (bytes):
 Capacity      Error-rate  Error-rate Error-rate Error-rate Error-rate Error-rate Error-rate Error-rate Error-rate Error-rate Error-rate Error-rate
               0.000000001 0.00000001 0.0000001  0.000001   0.00001    0.0001     0.001      0.01       0.02141585 0.1        0.5        0.99
 ------------- ----------- ---------- ---------- ---------- ---------- ---------- ---------- ---------- ---------- ---------- ---------- ----------
            10 54.48       48.49      42.5       36.51      30.52      24.53      18.53      12.54      10.56      6.553      2.366      0.5886

Tools.pm  view on Meta::CPAN

 z2z [-p -k -v -o -1 -2 -3 -4 -5 -6 -7 -8 -9 ] files

Converts (recompresses) files from one compression type to another. For instance from .gz to .bz2
Keeps uid, gid, mode (chmod) and mtime.

 -p              Show a progress meter using the pv program if installed
 -k              Keeps original file
 -v              Verbose, shows info on degree of compression and file
                 number if more than one file is being converted
 -o              Overwrites existing result file, otherwise stop with error msg
 -1 .. -9        Degree of compression, -1 fastest .. -9 best
 -e              With -t xz (or 2xz) passes -e to xz (-9e = extreme compression)

 -L rate         With -p. Slow down, ex:  -L 200K  means 200 kilobytes per second
 -D sec          With -p. Only turn on progress meter (pv) after x seconds
 -i sec          With -p. Info update rate
 -l              With -p. Line mode
 -I              With -p. Show ETA as time of arrival as well as time left
 -q              With -p. Quiet. Useful with -L to limit rate, but no output

The options -L -D -i -l -I -q implicitly turns on -p. Those options are passed