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##
## Copyright (C) 2004-2021 The Octave Project Developers
##
## See the file COPYRIGHT.md in the top-level directory of this
## distribution or <https://octave.org/copyright/>.
##
## This file is part of Octave.
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## -*- texinfo -*-
## @deftypefn {} {@var{y} =} spfun (@var{f}, @var{S})
## Compute @code{f(@var{S})} for the nonzero values of @var{S}.
##
## This results in a sparse matrix with the same structure as @var{S}.  The
## function @var{f} can be passed as a string, a function handle, or an
## inline function.
## @seealso{arrayfun, cellfun, structfun}
## @end deftypefn

function y = spfun (f, S)

  if (nargin != 2)
    print_usage ();
  endif

  [i, j, v] = find (S);
  [m, n] = size (S);

  if (is_function_handle (f))
    y = sparse (i, j, f(v), m, n);
  else
    y = 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]))
