strong.m

五点差分型多重网格方法：各种插值算子的比较）

function Si = strong(i,V,level)
% Determine the set of strong connections
% strong(I,V,level) returns the (sorted) set of strong connections
% of node I from the remaining set of free nodes V 
% with respect to matrix A at this level and the global treshold SW_BOUND.

% Ryan McKenzie
% Department of Computational Sciences
% University of Kentucky

%Adapted from a code by Dr. Gundolf Haase

amg_globals;

Ai = abs( A(level).matrix(i,:) );   % absolute values of row I in coefficient matrix
dim = size(Ai, 2); % number of coefficients to consider
aa=0; if i > 1,      aa=max(Ai(1:i-1)); end; %get point with maximum coefficient left of diagonal
bb=0; if i < dim,    bb=max(Ai(i+1:dim)); end; %get point with maximum coefficient right of diagonal
aimax = max(aa,bb); %get point with maximum coefficient

sk_set=[]; %initialize the strongly connected set to be empty
for k=V %consider each point in the domain
    if k~=i %do not consider connections to one's self...
       if sum(Ai(k))/aimax >= SW_BOUND %If the connection between points I and K is "strong enough"
           sk_set=union(sk_set,k); %add K to the strongly connected set of I
       end
    end
end
Si = sort(sk_set); %sort and return the strongly connected set of I