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del2

PURPOSE ^

%

SYNOPSIS ^

function D = del2 (M, varargin)

DESCRIPTION ^

% -*- texinfo -*-
% @deftypefn  {Function File} {@var{d} =} del2 (@var{m})
% @deftypefnx {Function File} {@var{d} =} del2 (@var{m}, @var{h})
% @deftypefnx {Function File} {@var{d} =} del2 (@var{m}, @var{dx}, @var{dy}, @dots{})
%
% Calculate the discrete Laplace
% @tex
% operator $( \nabla^2 )$.
% @end tex
% @ifnottex
% operator.
% @end ifnottex
% For a 2-dimensional matrix @var{m} this is defined as
%
% @tex
% $$d = {1 \over 4} \left( {d^2 \over dx^2} M(x,y) + {d^2 \over dy^2} M(x,y) \right)$$
% @end tex
% @ifnottex
% @example
% @group
%       1    / d^2            d^2         ...
% D  = --- * | ---  M(x,y) +  ---  M(x,y) | 
%       4    \ dx^2           dy^2        /
% @end group
% @end example
% @end ifnottex
%
% For N-dimensional arrays the sum in parentheses is expanded to include second derivatives 
% over the additional higher dimensions.
%
% The spacing between evaluation points may be defined by @var{h}, which is a
% scalar defining the equidistant spacing in all dimensions.  Alternatively, 
% the spacing in each dimension may be defined separately by @var{dx}, @var{dy},
% etc.  A scalar spacing argument defines equidistant spacing, whereas a vector
% argument can be used to specify variable spacing.  The length of the spacing vectors
% must match the respective dimension of @var{m}.  The default spacing value
% is 1.
%
% At least 3 data points are needed for each dimension.  Boundary points are
% calculated from the linear extrapolation of interior points.
%
% @seealso{gradient, diff}
% @end deftypefn

CROSS-REFERENCE INFORMATION ^

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