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.