## Copyright (C) 2004 David Bateman & Andy Adler
##
## This program 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 of the License, or
## (at your option) any later version.
##
## This program 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 this program; if not, write to the Free Software
## Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
## 02110-1301  USA

## -*- texinfo -*-
## @deftypefn {Function File} {@var{y} =} spfun (@var{f},@var{x})
## Compute @code{f(@var{x})} for the non-zero values of @var{x}.
## This results in a sparse matrix with the same structure as 
## @var{x}. The function @var{f} can be passed as a string, a
## function handle or an inline function.
## @end deftypefn

function t = spfun(f,s)
  if (nargin != 2)
    usage ("spfun(f,s)")
  endif

  if issparse(s)
    [i,j,v,m,n] = spfind(s);
  else
    [i,j,v] = find(s);
    [m,n] = size(s);
  end

  if (isa (f, "function handle") || isa (f, "inline function"))
    t = sparse(i,j,f(v),m,n);
  else
    t = sparse(i,j,feval(f,v),m,n);
  endif

endfunction

%!assert(spfun('exp',[1,2;3,0]),sparse([exp(1),exp(2);exp(3),0]))
%!assert(spfun('exp',sparse([1,2;3,0])),sparse([exp(1),exp(2);exp(3),0]))
%!assert(spfun(@exp,[1,2;3,0]),sparse([exp(1),exp(2);exp(3),0]))
%!assert(spfun(@exp,sparse([1,2;3,0])),sparse([exp(1),exp(2);exp(3),0]))