sor_smoother.m

五点差分型多重网格方法：各种插值算子的比较）

function [X_apx, iterations] = SOR_smoother(level, b, u_in)

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

amg_globals;
max_iter = ABSOLUTE_MAX_ITRS;
x = u_in;
er = [];
n = size(A(level).matrix,1);
D = diag(diag(A(level).matrix));
L = -tril(A(level).matrix,-1);
U = -triu(A(level).matrix,1);
normb = norm(b);

i = 1;
while (i <= max_iter)
  x = ((D-U)\L)*((D-L)\U)*x + ((D-U)\D)*((D-L)\b);
  if (normb)
    er = [er; norm(A(level).matrix*x - b)/normb];
  else
    er = [er; norm(x)];
  end
  if (STOP_TYPE==RESID_THRESHOLD)
      if( er(i) <= STOP_VALUE )
          break;
      end
  elseif (STOP_TYPE==RESID_REDUCE)
      if( er(i) <= (er(1) * STOP_VALUE) )
          break;
      end
  elseif (STOP_TYPE==MAX_ITRS)
      if( i >= STOP_VALUE )
          break;
      end      
  end
  i = i + 1;
end
iterations = i;
X_apx = x;