Bisection Algorithm
§(a) select an upper bound gu and a lower bound gl such that
§gl £ ||G||¥ £ gu 
• (b) if  (gu-gl)/gl £ specified level, stop; ||G||¥ » (gu+gl)/2. Otherwise go to next step.
• (c) set g  = (gl + gu) /2;
• (d) test if  ||G||¥ < g  by calculating the eigenvalues of H with this g;
• (e) if H has an eigenvalue on jR set gl = g ; otherwise set gu = g ; go back to step (b).
§In all the subsequent discussions, WLOG we can assume g  = 1 by a suitable scaling since ||G||¥ < g  Û    || g -1G||¥ <1.