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## or <https://octave.org/COPYRIGHT.html/>.
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## -*- texinfo -*-
## @deftypefn {} {} __fdjac__ (@var{fcn}, @var{x}, @var{fvec}, @var{typicalx}, @var{cdif}, @var{err})
## Undocumented internal function.
## @end deftypefn

function fjac = __fdjac__ (fcn, x, fvec, typicalx, cdif, err = 0)

  if (cdif)
    err = (max (eps, err)) ^ (1/3);
    h = err * max (abs (x), typicalx);
    fjac = zeros (length (fvec), numel (x));
    for i = 1:numel (x)
      x1 = x2 = x;
      x1(i) += h(i);
      x2(i) -= h(i);
      fjac(:,i) = (fcn (x1)(:) - fcn (x2)(:)) / (x1(i) - x2(i));
    endfor
  else
    err = sqrt (max (eps, err));
    signp = sign (x);
    signp(signp == 0) = 1;
    h = err * signp .* max (abs (x), typicalx);
    fjac = zeros (length (fvec), numel (x));
    for i = 1:numel (x)
      x1 = x;
      x1(i) += h(i);
      fjac(:,i) = (fcn (x1)(:) - fvec) / (x1(i) - x(i));
    endfor
  endif

endfunction