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## -*- texinfo -*-
## @deftypefn {} {@var{vars} =} symvar (@var{str})
## Identify the symbolic variable names in the string @var{str}.
##
## Common constant names such as @code{i}, @code{j}, @code{pi}, @code{Inf} and
## Octave functions such as @code{sin} or @code{plot} are ignored.
##
## Any names identified are returned in a cell array of strings.  The array is
## empty if no variables were found.
##
## Example:
##
## @example
## @group
## symvar ("x^2 + y^2 == 4")
## @result{} @{
##      [1,1] = x
##      [2,1] = y
##    @}
## @end group
## @end example
## @end deftypefn

function vars = symvar (str)

  warning ("off", "Octave:legacy-function", "local");  # using inline below.
  vars = argnames (inline (str));
  ## Correct for auto-generated 'x' variable when no symvar was found.
  if (numel (vars) == 1 && strcmp (vars{1}, "x") && ! any (str == "x"))
    vars = {};
  endif

endfunction


%!assert (symvar ("3*x + 4*y + 5*cos (z)"), {"x"; "y"; "z"})
%!assert (symvar ("sin ()^2 + cos ()^2 == 1"), {})
%!assert (symvar ("1./x"), {"x"})