function B = ddom6 (A,tol)
% B = ddom6 (A) returns a diagonally
% dominant matrix B by modifying the
% diagonal of A.
%
% This version is exceedingly slow.
%
% MATLAB Primer, 6th Edition
% Kermit Sigmon and Timothy A. Davis
% Section 8.5, page 43.

[m n] = size (A) ;
if (nargin == 1)
    tol = 100 * eps ;
end

for i = 1:n
    d = A (i,i) ;
    a = abs (d) ;
    f = 0 ;
    for j = 1:n
        if (i ~= j)
	    f = f + abs (A (i,j)) ;
	end
    end
    if (f >= a)
        aii = (1 + tol) * max (f, tol) ;
	if (d < 0)
	    aii = -aii ;
	end
	A (i,i) = aii ;
    end
end

B = A ;