/usr/share/octave/site/m/vlfeat/toolbox/imop/vl_dwaffine.m is in octave-vlfeat 0.9.17+dfsg0-6+b1.
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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 [dWx,dWy] = vl_dwaffine(x,y)
% VL_DWAFFINE Derivative of an affine warp
% [DWX,DWY]=VL_DWAFFINE(X,Y) returns the derivative of the 2-D affine
% warp [WX; WY] = [A T] [X; Y] with respect to the parameters A,T
% computed at points X,Y.
%
% See also: VL_WAFFINE(), VL_HELP().
% Copyright (C) 2007-12 Andrea Vedaldi and Brian Fulkerson.
% All rights reserved.
%
% This file is part of the VLFeat library and is made available under
% the terms of the BSD license (see the COPYING file).
% dW = [ kron(x',I) I ]
% |
% = [ x1 0 x2 0 1 0 ]
% [ 0 x1 0 x2 0 1 ]
z = zeros(length(x(:)),1) ;
o = ones(length(x(:)),1) ;
dWx = [ x(:) z y(:) z o z ] ;
dWy = [ z x(:) z y(:) z o ] ;
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