### Copyright (C) 1996 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.

## 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 

function y = conv (a, b)
  
  ## 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