# Description of the program: d2

This program estimates the correlation sum, the correlation dimension and the correlation entropy of a given scalar data set. It uses the box assisted search algorithm and is quite fast as long as one is not interested in large length scales. All length scales are computed simultaneously and the output is written every 2 min (real time not cpu time). It is possible to set a maximum number of pairs. If this number is reached for a given length scale, the length scale will no longer be treated for the rest of the estimate.

## Usage:

d2 [Options]

Everything not being a valid option will be interpreted as a potential datafile name. Given no datafile at all, means read stdin. Also - means stdin

Possible options are:

Option | Description | Default
--- | --- | ---
-l# | number of data points to be used | whole file
-x# | number of lines to be ignored | 0
-c# | column to read | 1
-d# | delay for the delay vectors | 1
-M# | maximal embedding dimension | 10
-t# | theiler window | 0
-E# | maximal length scale | 1 (data are rescaled to [0:1])
-e# | minimal length scale | 1e-3
-## | number of epsilon values | 100
-N# | maximal number of pairs to be used (0 means all possible pairs) | 1000
-o[#] | name of the output files (without extensions) | 'datafile'[.c2][.d2][.h2][.stat] (or if data were read from stdin: stdin[.c2][.d2][.h2][.stat])
-h | show these options | none

## Description of the Output:

The files with the extensions c2, d2 and h2 contain for each embedding dimension (from 1 to M) and each epsilon value three columns:
first column: epsilon (in natural units)
second column: the estimated quantity (correlation sum, dimension, entropy)
third column: epsilon (in rescaled units)
.

- extension .c2: This file contains the correlation sums for all treated length scales and embedding dimensions.
- extension .d2: This file contains the local slopes of the logarithm of the correlation sum, the correlation dimension.
- extension .h2: This file contains the correlation entropies.
- extension .stat: This file shows the current status of the estimate.

The output is written every two minutes (real time not cputime). So, you can see preliminary results even if the program is still running. Post-processing can be done using the program av-d2, but also c2d, c2t, and c2g.

View the C-source.

See also c2, c2naive, and c1

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