/usr/share/octave/site/m/vlfeat/toolbox/misc/vl_numder.m is in octave-vlfeat 0.9.17+dfsg0-6build1.
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1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 | function d = vl_numder(func, x, varargin)
% VL_NUMDER Numerical derivative
% D = VL_NUMDER(FUNC, X) computes the numerical derivative of the
% function FUNC at point X. X is a real array and is passed as first
% argument of FUNC.
%
% D = VL_NUMDER(FUNC, X, ARG1, ARG2, ...) passes ARG1, ARG2, ... as
% additional arguments to the function FUNC.
%
% See also: VL_NUMDER2(), VL_HELP().
% TODO: uniform sacaling of axis is not a good idea
dx = 1e-7 ;
N = numel(x) ;
fx = feval(func, x, varargin{:}) ;
d = zeros(length(fx(:)),N) ;
for n=1:N
e = zeros(size(x)) ; e(n) = 1 ;
fxn = feval(func, x+dx*e, varargin{:}) ;
di = (fxn - fx) / dx ;
d(:,n) = di(:) ;
end
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