Ubuntu Manpage: c-graph - visualization tool for the convolution theorem

Provided by: c-graph_2.0.1-3.1ubuntu2_amd64

NAME

       c-graph - visualization tool for the convolution theorem

SYNOPSIS

       c-graph [-d|-h|-v] [-n]

DESCRIPTION

GNU C-Graph (for Convolution Graph) is a tool for visualizing the convolution of two signals using
Gnuplot under the X Window System. It computes the linear convolution of two signals in the time domain,
then compares their circular convolution by demonstrating the convolution theorem - convolution of two
signals in the time domain corresponds to multiplication in the frequency domain. Gnuplot command and
graphics output files are saved in the c-graphs directory for later use.

Each signal is modeled by a register of discrete values simulating samples of a signal, and the discrete
Fourier transform (DFT) computed by means of the fast Fourier transform (FFT). FFTs are computed on data
series containing a power of two elements. c-graph accepts data series sizes of powers of two in the
range 64 to 1024, inclusive.

c-graph is menu-driven: it prompts the user for a number of samples, the signal type, frequency, and a
scaling coefficient (if applicable).

Data sets may consist of 64, 128, 256, 512, or 1024 samples. If any other data set size is chosen, the
size is adjusted to the nearest allowed power of two.

Signals may be periodic or aperiodic, according to input waveform type.

These signal types are periodic: sine, cosine, triangle, square, and sawtooth. Periodic signals can be
selected as continuous waves or as a pulse. If the pulse form is chosen, the input signal consists of a
half-wave of the signal type. For example, a sine wave chosen as a pulse will provide a sine wave of
half the full wave duration (i.e., from 0 to π radians, or 0 to 180°).

These signal types are aperiodic: exponential, ramp, and the step function.

The allowable frequency range is from 0.5 to N/4, where N is the number of samples. If a value is
entered outside of this range, the frequency is set to a default of 1 Hz.

The scaling coefficient may be positive or negative. The maximum absolute value of the scaling
coefficient for signal types sine, cosine, exponential, and the step function is N, whereas for signal
types triangle, square, sawtooth and ramp the maximum scale is 1. With the default scaling coefficient
of 1, signal types sine, cosine, exponential, and the step function are unit functions; signal types
square and sawtooth have a maximum amplitude of half the period, whereas that of a triangle is one-
quarter the period.

Whether student, engineer, or scientist, aspiring special-effects animator or roboticist, GNU C-Graph
will help you find the adventure in the mathematics of convolution.

OPTIONS

       -d, --dedicate
              Print the dedication and exit.

       -h, --help
              Print the list of options and exit.

       -n, --no-splash
              Invoke GNU C-Graph with no splash screen.

       -v, --version
              Print the version of GNU C-Graph and exit.

ENVIRONMENT VARIABLES

       GDFONTPATH
              This is the directory path that gnuplot(1) searches for fonts  to  produce  its  graphs.   c-graph
              commands  gnuplot  to use a font named "serif".  If gnuplot does not find this font, it will use a
              default.  To select the gnuplot font, create a symbolic link from the desired font file to a  file
              named  "serif.ttf".   Then  set  GDFONTPATH  to  the  directory where "serif.ttf" is located.  For
              example if the file /home/galactic/fonts/serif.ttf links to the desired serif font,  then  in  the
              Bourne shell use a command such as the following:

                   export GDFONTPATH=/home/galactic/fonts:/usr/share/fonts

FILES

       Upon  exit, c-graph saves its sample sets and graphics files in the c-graphs directory within the current
       working directory.  Here is a typical recursive listing of the output directory contents:

            $ ls -R c-graphs
            c-graphs:
            coms  graphs

            c-graphs/coms:
            convolutions.cg  signals.cg  time.dat  trans.dat  transforms.cg

            c-graphs/graphs:
            convolutions.png  signals.png  transforms.png

       The c-graphs/coms directory contains the input for Gnuplot that was used to generate the output graphics.
       Files ending in ".cg" are Gnuplot command files.  Files ending in ".dat" are ASCII data input files; they
       are tables of floating point values of input waveforms.

       The c-graphs/graphs directory contains the graphics output of Gnuplot, in Portable Network Graphics (PNG)
       format.   These  files  can  be  used  in  presentations  and other documents to visually demonstrate the
       convolution theorem.

BUGS

       Report bugs to agt@codeartnow.com.

AUTHOR

       GNU C-Graph was written by Adrienne Gaye Thompson (agt@codeartnow.com).  This package  evolved  from  the
       BSc.  Electrical  Engineering  honours  dissertation  of Adrienne Thompson, "Interactive Computer Program
       Demonstrating: Sampling Convolution and the FFT", University of Aberdeen, Scotland (1983).

COPYRIGHT

       Copyright © 1982, 1983, 1996, 2008, 2009, 2010, 2011, 2018 Adrienne Gaye Thompson.

       GNU C-Graph is licensed under the GPL version 3 or later with Additional Terms  as  permitted  under  the
       GPL;  see  the  COPYING  file  in  this  package  for  details.   For  the latest version of the GPL, see
       http://gnu.org/licenses/gpl.html.

       This is free software; you are free to modify and distribute it.  There is NO  WARRANTY,  to  the  extent
       permitted by law.