From octave-sources-request at bevo dot che dot wisc dot edu  Wed Dec 20 15:34:20 2000
Subject: improved conv.m
From: "Johan Kullstam" <kullstam at ne dot mediaone dot net>
To: octave-sources at bevo dot che dot wisc dot edu
Date: 20 Dec 2000 16:36:28 -0500


conv.m can do convolution of two vectors

x = conv(a,b)

since the convolution operation is associative, we can allow more
vectors

y = conv(a,b,c) = conv(conv(a,b),c) = conv(a,conv(b,c))

this new version uses varargs to process one or more vectors.
it is fully backwards compatible with the old version.  i'd like to
have this version go into the standard library of octave m-files.

enjoy.

johan

## Copyright (C) 1996, 1997 John W. Eaton
##
## This file is part of Octave.
##
## Octave is free software; you can redistribute it and/or modify it
## under the terms of the GNU General Public License as published by
## the Free Software Foundation; either version 2, or (at your option)
## any later version.
##
## Octave is distributed in the hope that it will be useful, but
## WITHOUT ANY WARRANTY; without even the implied warranty of
## MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
## General Public License for more details.
##
## You should have received a copy of the GNU General Public License
## along with Octave; see the file COPYING.  If not, write to the Free
## Software Foundation, 59 Temple Place - Suite 330, Boston, MA
## 02111-1307, USA.

## -*- texinfo -*-
##  at deftypefn {Function File} {} conv (@var{a}, @var{b}, ...)
## Convolve one or more vectors.
##
##  at code{y = conv (a, b)} returns a vector of length equal to
##  at code{length (a) + length (b) - 1}.
## If  at var{a} and @var{b} are polynomial coefficient vectors, @code{conv}
## returns the coefficients of the product polynomial.
##
##  at code{y = conv (a, ...)} returns the convolution of one or more vectors.
##  at end deftypefn
##  at seealso{deconv, poly, roots, residue, polyval, polyderiv, and polyinteg}

## Author: Tony Richardson <arichard at stark dot cc dot oh dot us>
## Created: June 1994
## Adapted-By: jwe
##
## Dec 2000 Johan Kullstam <kullstam at ne dot mediaone dot net>
## do multiple convolution

function a = conv(a,...)
  ## Ensure that all inputs are vectors.
  if (!is_vector(a))
    error("conv: all arguments must be vectors");
  endif
  ## Ensure that all vectors are row vectors.
  ## and get the length in the meantime.
  [r,c] = size(a);
  if r > 1,
    la = r;
    a = reshape (a, 1, la);
  else
    la = c;
  endif
  va_start();
  ## loop over all inputs
  while (--nargin)
    b = va_arg();
    ## Ensure that all inputs are vectors.
    if (!is_vector(b))
      error("conv: all arguments must be vectors");
    endif
    ## Ensure that all vectors are row vectors.
    ## and get the length in the meantime.
    [r,c] = size(b);
    if r > 1,
      lb = r;
      b = reshape(b, 1, lb);
    else
      lb = c;
    endif

    ## Use the shortest vector as the coefficent vector to filter.
    ly = la + lb - 1;
    if (la < lb)
      if (ly > lb)
	x = [b, (zeros(1, ly-lb))];
      else
	x = b;
      endif
      a = filter(a, 1, x);
    else
      if (ly > la)
	x = [a, (zeros(1, ly-la))];
      else
	x = a;
      endif
      a = filter(b, 1, x);
    endif
    la = ly;
  endwhile
endfunction


-- 
J o h a n  K u l l s t a m
[kullstam at ne dot mediaone dot net]
Don't Fear the Penguin!



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