'\"
'\" Generated from file 'filtergen\&.man' by tcllib/doctools with format 'nroff'
'\" Copyright (c) 2020 by Arjen Markus
'\"
.TH "math::filters" 3tcl 0\&.1 tcllib "Tcl Math Library"
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.SH NAME
math::filters \- Digital filters
.SH SYNOPSIS
package require \fBTcl  8\&.6\fR
.sp
package require \fBTclOO \fR
.sp
package require \fBmath::filters  ?0\&.1?\fR
.sp
\fB::math::filters::filterButterworth\fR \fIlowpass\fR \fIorder\fR \fIsamplefreq\fR \fIcutofffreq\fR
.sp
\fB::math::filters::filter\fR \fIcoeffs\fR \fIdata\fR
.sp
\fB::math::filters::filterObj\fR new \fIcoeffs\fR \fIyinit\fR
.sp
\fB$filterObj\fR filter \fIx\fR
.sp
\fB$filterObj\fR reset
.sp
.BE
.SH DESCRIPTION
.PP
The \fBmath::filters\fR package implements digital filters,
notably Butterworth low-pass and high-pass filters\&. The procedures
allow to filter an entire data series as well as filter data one
by one\&.
.SH PROCEDURES
The package defines the following public procedures:
.TP
\fB::math::filters::filterButterworth\fR \fIlowpass\fR \fIorder\fR \fIsamplefreq\fR \fIcutofffreq\fR
Determine the coefficients for a Butterworth filter of given order\&. The coefficients are returned as
a list of the x-coefficients, the y-coefficients and the scale\&. The formula is (n is the filter order):
.CS


                   n             n
    scale * y_k = sum x_(k-i) + sum y_(k-i)
                  i=0           i=1

.CE
.RS
.TP
bool \fIlowpass\fR
Generate a low-pass filter (1) or a high-pass filter (0)
.TP
integer \fIlowpass\fR
The order of the filter to be generated
.TP
double \fIsamplefreq\fR
Sampling frequency of the data series
.TP
double \fIcutofffreq\fR
Cut-off frequency for the filter
.RE
.TP
\fB::math::filters::filter\fR \fIcoeffs\fR \fIdata\fR
Filter the entire data series based on the filter coefficients\&.
.RS
.TP
list \fIcoeffs\fR
List of coefficients as generated by \fIfilterButterworth\fR (or in fact any similar list of coefficients)
.TP
list \fIdata\fR
Data to be filtered
.RE
.TP
\fB::math::filters::filterObj\fR new \fIcoeffs\fR \fIyinit\fR
Create a filter object\&. The initial x data are taken as zero\&. The initial y data can be prescribed\&. If they are not given,
they are taken as zero as well\&.
.RS
.TP
list \fIcoeffs\fR
List of coefficients as generated by \fIfilterButterworth\fR (or in fact any similar list of coefficients)
.TP
list \fIyinit\fR
(Optional) initial data for the filter result\&.
.RE
.TP
\fB$filterObj\fR filter \fIx\fR
Filter a single value and return the result\&.
.RS
.TP
double \fIx\fR
The value to be filtered
.RE
.TP
\fB$filterObj\fR reset
Reset the filter object (start anew)
.PP
.SH KEYWORDS
digital, filtering
.SH CATEGORY
Mathematics
.SH COPYRIGHT
.nf
Copyright (c) 2020 by Arjen Markus

.fi