view man/man1/racf.1 @ 0:5242703e91d3 tip

Initial checkin for AIM92 aimR8.2 (last updated May 1997).

.TH RACF 1 "1 September 1993"

.SH NAME
racf \- recursive autocorrelation function of contiguous frames.

.SH SYNTAX 
racf  [arguments]  [file]

.SH DESCRIPTION
Autocorrelation function using a recursive "leaky integrator" filter.
For the m'th lag, the n'th recursive update is:

.nf
      y[n] = a.y[n-1] + (1-a).f[n].f[n-m]
.fi

where decay constant a = exp(-Ts/T),
Ts is the sample interval in seconds, and T  is the decay time constant in seconds.

The recursion computes the mean value of the product f[n].f[n-m]
within an exponential window which weights past values.
The window width parameter (eg. corresponding with the width of the
fft analysis window) is the time constant parameter.
The half life of the exponential window is given by -T.ln(0.5) = 0.693T
ie. for a given time constant, T secs, the window decays to half of its
current value in a period of 0.693T secs.
Similarly, the window decays by 99% of its initial value in about 4.6T secs.
So T can be set to accomodate an expected period.

The routine generates the autocovariance function.
An optional normalization (dividing each coefficient by the zeroth
coefficient) produces the autocorrelation function,
(and this is then scaled up to the range [0-1000]).

The output framewidth is the given maximum acf lag.

.SH "SEE ALSO"
options acf acgram

.SH COPYRIGHT
.LP
Copyright (c) Applied Psychology Unit, Medical Research Council, 1995
.LP
Permission to use, copy, modify, and distribute this software without fee 
is hereby granted for research purposes, provided that this copyright 
notice appears in all copies and in all supporting documentation, and that 
the software is not redistributed for any fee (except for a nominal 
shipping charge). Anyone wanting to incorporate all or part of this 
software in a commercial product must obtain a license from the Medical 
Research Council.
.LP
The MRC makes no representations about the suitability of this 
software for any purpose.  It is provided "as is" without express or 
implied warranty.
.LP
THE MRC DISCLAIMS ALL WARRANTIES WITH REGARD TO THIS SOFTWARE, INCLUDING 
ALL IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS, IN NO EVENT SHALL 
THE A.P.U. BE LIABLE FOR ANY SPECIAL, INDIRECT OR CONSEQUENTIAL DAMAGES 
OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, 
WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, 
ARISING OUT OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS 
SOFTWARE.