# Copyright (C) 1995 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, 675 Mass Ave, Cambridge, MA 02139, USA.

function y = conv (a, b)
  
# usage: conv (a, b)
#
# Convolve two vectors.
#
# y = conv (a, b) returns a vector of length equal to length (a) +
# length (b) -1.
#
# If a and b are polynomial coefficient vectors, conv returns the
# coefficients of the product polynomial.
#
# SEE ALSO: deconv, poly, roots, residue, polyval, polyderiv, polyinteg 

# Written by Tony Richardson (amr@mpl.ucsd.edu) June 1994.

  if (nargin != 2)
    usage ("conv(a, b)");
  endif

  if (is_matrix (a) || is_matrix (b))
    error("conv: both arguments must be vectors");
  endif

  la = length (a);
  lb = length (b);

  ly = la + lb - 1;

  # Ensure that both vectors are row vectors.
  if (rows (a) > 1)
    a = reshape (a, 1, la);
  endif
  if (rows (b) > 1)
    b = reshape (b, 1, lb);
  endif

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

endfunction