function y = sqrtN2(x,guess)
% iterate:
% y = guess - ( ((guess^2)-x) / 2*guess)
oldguess = guess + 1;
while (guess ~= oldguess)
disp(sprintf('guess-oldguess=%.20f', guess-oldguess))
oldguess = guess;
guess = guess - (((guess^2)-x)/(2*guess));
end
y = guess;
end