del2_9pt.m

matlab 九点差分源代码,可以直接运行

function [output]=del2_9pt(input,delx);
% DEL2_9PT ... compute the 9 point Laplacian
% 
% [output]=del2_9pt(input,delx)
%
% DEL2_9PT computes the 9 point approximation to the laplacian operator of 
% the two dimensional matrix 'input'.  The horizontal and vertical bin
% spacing of the matrix must be the same.  
%
% input = input matrix
% delx = the horizontal/ vertical bin spacing in consistent units
%
% output = the output matrix

[nrows,ncolumns]=size(input);

input2=zeros(nrows+4,ncolumns+4);
input2(3:nrows+2,3:ncolumns+2)=input;

% create output matrix
output=zeros(nrows,ncolumns);

% for first dimension

  output = (-input2(1:nrows,3:ncolumns+2) ...
            + 16*input2(2:nrows+1,3:ncolumns+2) ...
            -30*input2(3:nrows+2,3:ncolumns+2)...
            + 16*input2(4:nrows+3,3:ncolumns+2) ... 
            -input2(5:nrows+4,3:ncolumns+2))/(12*delx^2);

% for second dimension 

input2=input2.';
output=output.';

 output = (-input2(1:ncolumns,3:nrows+2) + 16*input2(2:ncolumns+1,3:nrows+2) ...
                 -30*input2(3:ncolumns+2,3:nrows+2) + 16*input2(4:ncolumns+3,3:nrows+2) ...
                 -input2(5:ncolumns+4,3:nrows+2))/(12*delx^2) + output;
output=output.';