filterDoog

 n-dim difference of offset Gaussian DooG filter (Gaussian derivative).

 Creates a nd derivative of Gaussian kernel.  For all but d==1 use
 primarily for visualization purposes -- for filtering better to use the
 indvidiual seperable kernels for efficiency purposes.

 USAGE
  dG = filterDoog( dims, sigmas, nderivs, [show] )

 INPUTS
  dims    - nd element vector of dimensions of final Gaussian
  sigmas  - sigmas for nd Gaussian
  nderivs - order of derivative along each of the nd dimensions
  show    - [0] figure to use for optional display

 OUTPUTS
  dG      - The derivative of Gaussian filter

 EXAMPLE
  dG1 = filterDoog( 43, 2, 3, 1 ); %1D
  dG2 = filterDoog( [41 41], [3 3], [1,1], 2 ); %2D
  dG3 = filterDoog( [101 101 101], [4,4,10], [1,1,0], 3 ); %3D

 See also FILTERGAUSS, NORMPDF2, FILTERDOG2D, FILTERGABOR2D

 Piotr's Computer Vision Matlab Toolbox      Version 2.0
 Copyright 2014 Piotr Dollar.  [pdollar-at-gmail.com]
 Licensed under the Simplified BSD License [see external/bsd.txt]